Convocation 2007

 
A few months ago I told you about my first convocation as a Professor [Bruce Alberts in Toronto]. Here's the formal photograph of the main participants. Don't we look pretty?

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Monday's Molecule #58

 
This is one example of a very common molecule found in every cell. You have to give us the common name of this molecule and identify the species. You'll be pleased to know that I don't need the systematic IUPAC name for this one.

There's a direct connection between this molecule and Wednesday's Nobel Laureate. Your task is to figure out the significance of today's molecule and identify the Nobel Laureate who studied its function. (Hint: The Nobel Laureate is a Canadian—there aren't very many Canadian Nobel Laureates so this is a very big hint.)

The reward goes to the person who correctly identifies the molecule and the Nobel Laureate. Previous winners are ineligible for one month from the time they first collected the prize. There is one ineligible candidates for this week's reward because Sandwalk readers were not very successful in December. The prize is a free lunch at the Faculty Club.

THEME:

Nobel Laureates
Send your guess to Sandwalk (sandwalk(at)bioinfo.med.utoronto.ca) and I'll pick the first email message that correctly identifies the molecule and the Nobel Laureate. Note that I'm not going to repeat Nobel Laureates so you might want to check the list of previous Sandwalk postings.

Correct responses will be posted tomorrow along with the time that the message was received on my server. I may select multiple winners if several people get it right.

Comments will be blocked for 24 hours. Comments are now open.

UPDATE: We have a winner! This one proved to be far more difficult than I imagined. Everyone got the Nobel Laureate (Sidney Altman) but very few people got the molecule correct. Some people failed to identify the species correctly even though I specifically asked for the species. Most people said that the molecule is RNase P but that isn't quite correct.

The molecule is the M1 RNA subunit of RNase P from E. coli. The other subunit is a small protein called the C5 protein cofactor. This RNA is sometimes called RNA P and that would have been an acceptable answer.

Only one person got everything right and that response just arrived a few minutes ago. Congratulations to PonderingFool for knowing that the molecule was the M1 RNA component of E, coli RNase P and the Nobel Laureate is Sidney Altman.

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Creation Science Papers

 
Phil Plait of Bad Astronomy must have had a great deal of free time on his hands now that the asteroids have missed us and the galaxy isn't going to be consumed by a hydrogen cloud for at least 40 million years. He was thinking of writing a paper for a new journal sponsored by Answers in Genesis [Creationists: publish and perish].

Phil was interested in the first two papers that were published in the Answers Research Journal. One was a geology paper and one was about microbiology. Phil wanted to know how good they were.

Being as relieved as him about the fact that the Earth survived the near miss, I decided I could spare a few minutes to read the microbiology article. It's by Alan L. Gillen from that famous center of research called Liberty University. Here's the abstract.

The world of germs and microbes has received much attention in recent years. But where do microbes fit into the creation account? Were they created along with the rest of the plants and animals in the first week of creation, or were they created later, after the Fall. These are some questions that creation microbiologists have been asking in recent years. Ongoing research, based on the creation paradigm, appears to provide some answers to these puzzling questions. The answers to these questions are not explicit in Scripture, so the answers cannot be dogmatic. However, a reasonable extrapolation from biological data and Scripture can be made about the nature of microbes in a fully mature creation. This article attempts to provide reasonable answers to when microbes were created and is meant to stimulate discussion and further research in this area.

Very little has been written in Bible commentaries or in creation literature on the subject of when microbes were created. Some have postulated that microbes were created on a single day of Creation, such as Day Three—when the plants were made. This is partially due to the “seed-like” characteristics that bacteria and fungi have—therefore classifying microbes as plants. In addition, we observe microbes (such as Escherichia coli) isolated in the lab and we tend to think of microbes as individual entities much like birds or fish or animals and, therefore, created on a single day. However, in nature, the vast majority of microbes live in biological partnerships, not in total isolation. The natural symbiosis of microbes with other creatures is the norm. Therefore, we postulate that microbes were created as “biological systems” with plants, animals, and humans on multiple days, as supporting systems in mature plants, animals, and humans. This idea is further supported by the work of Francis (2003). Francis calls microbial symbiotic systems a biomatrix, or organosubstrate. He proposes that microbes were created as a link between macroorganisms and a chemically rich but inert physical environment, providing a surface (i.e., substrate) upon which multicellular creatures can thrive and persist in intricately designed ecosystems. From the beginning, God made His creation fully mature, and complex forms fully formed. This would insure continuity and stability for the times to come. Although we cannot be certain as to specifically when the Creator made microbes, it is within His character to make entire interwoven, “packaged” systems to sustain and maintain life.

I didn't read any further.

Phil, the bad news is that this is a pile of crap. The good news is that you won't have to waste very much time writing a paper for this journal. You can probably knock it off in an afternoon.

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[Image Credit: The Complete Idiot’s Guide to Just Doing It]

Scientific Illiteracy About Death Rates

 
Here's part of an article on ScienceDaily about death rates in New York City [New York City Death Rate Reaches Historic Low].

The death rate in New York City reached an all-time low in 2006, the Health Department reported today, as the number of deaths fell to 55,391 -- down from 57,068 in 2005 and 60,218 in 2001. Mortality declined in eight leading categories, including diabetes, HIV, chronic lung disease and kidney failure. The only leading killer that increased significantly was substance use (up 8%). Heart disease and cancer remained the city's biggest killers, claiming 21,844 lives and 13,116 lives, respectively. The figures come from the latest Annual Summary of Vital Statistics, the definitive registry of births and deaths in New York City.

The numbers of deaths are not death rates. This is one of my pet peeves. I get angry when newspaper reporters screw it up but this is much worse. It's from a website that's supposed to specialize in science ("Your Source for the Latest Research News").

The raw numbers are available at Summary of Vital Statistics 2006: The City of New York. They show that the death rate did, indeed, fall from 7.0 per 1000 citizens in 2004 to 6.7 per 1000 citizens in 2006. In 1916 it was 14.0 while in 1980, 1990, and 2000 it was 10.0, 10.1, and 7.6 respectively.

The absolute numbers of deaths tells you nothing about death rates. For all we know, the population of New York City could have fallen from 2004 to 2006 and the death rate could have gone up. (Incidentally, if you look at the raw data you'll see an interesting footnote. The rates in 2004-2006 were revised downwards when the 2007 census data for population was used. Previous estimates were based on the population according to the 2000 census.)

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[Image Credit: New York City in 1916 from The University of Texas at Austin]

Scientific Mistakes

 
During a recent discussion with undergraduates, they mentioned that it would be a good idea to discuss the more recent scientific papers in class. They seemed to be very impressed with a course that presented papers published within the past few months.

I pointed out that there's a problem with that kind of course. If the goal of a course is to teach fundamental principles and concepts then it's very unlikely that recent papers are going to advance that goal. Why is that? Because much of the scientific literature is either trivial or incorrect. You don't know that it's trivial or incorrect until some time has passed and other scientists react.¹

If the goal of a course is to teach how science is done on a day-to-day basis, then a key part of that course should be to drive home the concept of skepticism. Don't believe everything you read in the latest journals. An important part of that teaching goal is to pick examples of important mistakes in older literature.

John Dennehy has helped us out this week by posting a "citation classic" that turned out to be wrong [This Week's Citation Classic: Being Wrong]. In my opinion, it's far more important to look at examples like this than to expose undergraduates to several dozen hot new papers that are supposedly at the cutting edge.

The paper that John choose is by Paul Boyer who subsequently won the Nobel Prize in Chemistry [Nobel Laureates: Paul Boyer and John Walker] for his work on the mechanism of ATP synthase [How Cells Make ATP: ATP Synthase].

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1. Sometimes it takes a long time for scientists to react to mistakes in the literature. Wrong ideas can be perpetuated for decades after they've been refuted, especially if the original papers were widely referenced. I was reminded of this the other day when listening to a graduate student seminar—coincidently, on the structure of ATP synthase. The student posted an old-fashioned, out-of-date view of the citric acid cycle as an introduction to the function of ATP synthase. I have challenged my undergraduate biochemistry class to find a single example of a web site that gets the entire citric acid cycle correct. There's a prize. They can't use the IUBMB site, they can't use my sites, and they can't make one of their own. So far nobody has collected the prize.

How Much Junk in the Human Genome?

Ryan Gregory has another contribution to this question that's well worth a read [Is most of the human genome functional?].

Among other things, Ryan picks on the views of John Mattick who has got to be one of the worst scientists in the field. Whenever I read a paper by Mattick I revise my opinion of the value of peer-reviewed literature. It's bad enough that Mattick has silly ideas but it's even sadder that his "peer" reviewers don't recognize it.

Here's a quote from Mattick that I discussed in my article on the The Central Dogma of Molecular Biology. It's obvious that he doesn't understand the real meaning of the central dogma. Can you pick out the other conceptual flaws in this paragraph? [Hints: Worst Figure Ever and Dog Ass Plots.]

The central dogma of biology holds that genetic information normally flows from DNA to RNA to protein. As a consequence it has been generally assumed that genes generally code for proteins, and that proteins fulfil not only most structural and catalytic but also most regulatory functions, in all cells, from microbes to mammals. However, the latter may not be the case in complex organisms. A number of startling observations about the extent of non-protein coding RNA (ncRNA) transcription in the higher eukaryotes and the range of genetic and epigenetic phenomena that are RNA-directed suggests that the traditional view of genetic regulatory systems in animals and plants may be incorrect.

Mattick, J.S. (2003) Challenging the dogma: the hidden layer of non-protein-coding RNAs in complex organisms. BioEssays 25:930-939.

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Graduate Students Need to Publish Papers

 
In my field it takes five, or even six, years to complete a Ph.D. program. This time could be significantly reduced if there wasn't pressure on students to produce publishable work. The reduction in time is even more obvious at the M.Sc. level where it often take far more than two years to get a degree.

One could make a case for an M.Sc. degree that was not a "research" oriented degree. These programs would be useful for high school teachers, for example, or patent attorneys, or even physicians.

But those are exceptions. In most research departments the thesis is based on scientific research. Does that research have to produce results that can be published in the scientific literature? Yes it does.

T. Ryan Gregory explains why [Why would advisors encourage students to publish?]. (This is a repost of an article that he published earlier on Genomicron but it's still relevant and topical, especially in our department where we are grappling with the issue of long times to completion.)

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[Photo Credit: Graduate students in the Department of Biochemistry 2007-2008.]

Test Your God Logic

 
Here's a quiz you can try to see if your positions on atheism and religion are consistent [Battleground God]. Be careful, this quiz has many pitfalls. I took three hits and a bullet but it's not because I'm illogical, in my opinion. It's because questions can be interpreted in several different ways.

Here's one of the questions that caused me trouble.

It is foolish to believe in God without certain, irrevocable proof that she exists.

I answered "true." What I mean by that is that you require evidence to believe in something. What the authors of the study mean is that "certain, irrevocable proof" is inconsistent with my answer about evolution! They say,

You stated earlier that evolutionary theory is essentially true. However, you have now claimed that it is foolish to believe in God without certain, irrevocable proof that she exists. The problem is that there is no certain proof that evolutionary theory is true - even though there is overwhelming evidence that it is true. So it seems that you require certain, irrevocable proof for God's existence, but accept evolutionary theory without certain proof. So you've got a choice:

Bite a bullet and claim that a higher standard of proof is required for belief in God than for belief in evolution.

Take a hit, conceding that there is a contradiction in your responses.

I did, indeed, reply "true" to the statement that evolutionary theory is essentially true. But that's only because I wasn't given the option of replying to the statement that evolution is a fact. I accept evolution because there is certain proof that it exists. I assumed, incorrectly as it turns out, that they were using "evolutionary theory" as a synonym for "evolution."

In order to be consistent I guess I should have replied that "evolutionary theory" is not essentially true.

Watch out for Question 15. It's also a trap.

Read the comments on FriendlyAtheist. Quite a few people got through the test with no hits. I wonder how they answered the question about evolution.

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Vegetarian Humor

 
Today after class we were having a wide-ranging discussion about all kinds of issues when one of my students announced that she was a vegan. She claimed that all us meat-eaters were ignoring the slaughter of animals required to justify our habit.

I retorted with the standard reply that she was conveniently ignoring all the plants that had to die for her. Her response caught me off-guard—it was new to me but may be old hat to you. Anyway, she said, "I'm not vegan because I love animals, I'm a vegan because I hate plants!"

The original quote is ...

I am not a vegetarian because I love animals; I am a vegetarian because I hate plants.

                                             A. Whitney Brown

I like it. From now on I'll say that I'm an omnivore because I hate all living things!

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The photo honors National Meatloaf Appreciation Day. At least one animal, and several plants, were seriously injured during the making of this photo.

Electoral Compass

 
I'm a sucker for these things but take them with a huge grain of salt because I'm not an American. Some of the questions were very difficult to answer and I ended up having to guess what they wanted a socialist like me to say.

Why isn't Kucinich on the chart? How accurate are the positions of the candidates?

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Stop the Presses! Denyse O'Leary Says Something Thruthful!

 
You'd better sit down before I tell you this. Over on Uncommon Descent Denyse O'Leary has just posted an article complaining about evolution, as Intelligent Design Creationists tend to do¹ [Today at Design of Life: The Avalon explosion: Another intricate, Darwin-busting puzzle].

But she really blows it in the first sentence when she accidentally gets something right, suggesting that she is finally beginning to understand what we've been telling her for years.

Contrary to popular misconceptions, the history of life shows no steady Darwinian march of progress ...

Congratulations, Denyse. You finally understand that there's no progress in evolution. There's no purpose either.

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1. They think that criticism of evolution is the same as promoting Intelligent Design Creationism—but then, that's why we call them IDiots.

What's Going On Here ?

 


Go to easternblot to find out. The photos were taken in the 2nd year introductory Cell and Molecular Biology course at the University of Toronto.

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Drinking Cold Water Causes Cancer

 

Friday's Urban Legend: FALSE

This one was sent to me a few days ago.

This is a very good article. Not only about the warm water after your meal, but about heart attacks. The Chinese and Japanese drink hot tea with their meals, not cold water, maybe it is time we adopt their drinking habit while eating.

For those who like to drink cold water, this article is applicable to you. It is nice to have a cup of cold drink after a meal. However, the cold water will solidify the oily stuff that you have just consumed. It will slow down the digestion. Once this "sludge" reacts with the acid, it will break down and be absorbed by the intestine faster than the solid food. It will line the intestine. Very soon, this will turn into fats and lead to cancer. It is best to drink hot soup or warm water after a meal.

A serious note about heart attacks - You should know that not every heart attack symptom is going to be the left arm hurting. Be aware of intense pain in the jaw line.

You may never have the first chest pain during the course of a heart attack. Nausea and intense sweating are also common symptoms. 60% of people who have a heart attack while they are asleep do not wake up. Pain in the jaw can wake you from a sound sleep. Let's be careful and be aware. The more we know, the better chance we could survive.

A cardiologist says if everyone who reads this message sends it to 10 people, you can be sure that we'll save at least one life. Read this & Send to a friend. It could save a life.

So, please be a true friend and send this article to all your friends you care about.

Snopes.com checked it out and guess what? It's not true [Cold Comfort].

The email message originated only two years ago (February, 2006) so it's a relatively recent urban legend.

One of the tests I recommend when you receive free medical advice on the internet is to ask yourself whether your doctor gives out the same advice. If so, then it may be true. But you would already suspect that since your doctor told you.

If your doctor never told you about the email warning then there are three possibilities ...

1. Your doctor doesn't know about this important problem that could cause cancer but all your friends and neighbours do know about it.


2. Your doctor has heard the story but knows that it's false.


3. Your doctor knows that cold liquids cause cancer (or whatever) but for some reason doesn't want you to know this so she won't tell you.

Ask yourself which possibility is most likely?

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[Photo Credit: [FreeFoto.com]

Student Evaluations

Yesterday we had a departmental retreat where we discussed a number of things, including undergraduate education. The Biochemistry Undergraduate Student Society (BUSS) made a presentation and sent along eight students who joined the various discussion groups that we set up to talk about undergraduate teaching. It was lots of fun and very informative.

One of the issues that was raised was student evaluations. The main student group for all arts students and science students has a standard student evaluation form that they distribute in most classes. The results are published in the Anti-Calendar.

The Department of Biochemistry does not participate in this exercise and, consequently, none of our courses are in the Anti-calendar. We use our own evaluation forms with very different questions and the results are summarized for internal use within the department.

Some students suspect that the department has blocked the publication of student evaluations in the Anti-Calendar. They suspect that the reason for doing this is all of our courses have very bad ratings and we don't want students to find out how bad we are. (That kind of reasoning may actually work in our favor. Students who think like that stay out of our courses.)

The truth is that we have been doing our own evaluations for 40 years and we have different questions, and a different scale, than the ones used by the student union. That's the only reason why we're not in the Anti-Calendar.

However, even if we switched to using the standard students forms, I would remain opposed to collecting and publishing student evaluations for another reason. (The following opinion is not departmental policy, unfortunately.)

I've blogged about this is the past [Student Evaluations] [Student Evaluations Don't Mean Much]. The facts are that student evaluations don't evaluate what students think they're evaluating. Many scientific studies have been done and the evidence strongly suggests that students evaluations are based mostly on whether students like the personality of the Professor.

I teach science and scientific reasoning. I think it's important to ask whether the collecting and publication of student evaluations is a worthwhile and valid exercise. If student evaluations are scientifically justified then they should be published. If the evidence doesn't back up the claims then they are worthless. This isn't hard to follow, is it?

Publication of worthless student evaluations may actually be counter-productive. The result may turn students away from courses they should be taking and encourage them to take easy bird courses they should be avoiding.

Until it can be demonstrated that student evaluations are useful and scientifially valid, I will continue to exercise my right to block publication of my evaluations, regardless of any decision by the Department of Biochemistry. And I will continue to argue against using flawed student evaluations in tenure and promotion decisions. I will also oppose all attempts to reward faculty members for excellence in teaching based entirely—or mostly—on student evaluations. Any other position is anti-scientific, in my opinion. No competent scientist can ever justify relying on standard undergraduate student evaluations to evaluate teaching ability.

Let's hear what everyone else thinks of student evaluations.

Here are a few interesting links to stimulate discussion.

Part of the discussion requires that you understand the "Sandbox Experiment" as described in [Of What Value are Student Evaluations?].

... true believers (who too often seem to have a stake in selling institutions a workshop or an evaluation form) proclaim that student evaluations cannot be manipulated or subverted. Anyone who believes such claims needs to read the first part of Generation X Goes to College by Peter Sacks. This part is an autobiography of a tenure track experience by the author in an unnamed community college in the Northwest. Sacks, an accomplished journalist who is not a very accomplished teacher, soon finds himself in trouble with student evaluations. Sacks exploits affective factors to deliberately obtain higher evaluations, and describes in detail how he did it in Part 1 called "The Sandbox Experiment." Sacks obtains higher evaluations through a deliberate pandering, but not through promotion of any learning outcomes. For years, he manages not only to deceive students, but also peers and administrators and eventually gets tenure based on higher student evaluations. This is a brutal case study that many could find offensive, but it proves clearly that (1) student evaluations can indeed be manipulated, and (2) that faculty peer reviewers and administrators who should know better than to place such blind faith in student evaluations sometimes do not.

Read Student Evaluations: A Critical Review for a description of the Dr. Fox Effect, another one of those standard examples that every one should be aware of if they want to debate the issue of student evaluations.

This article also has a pretty good discussion of the "academic freedom" issue—which I prefer to call the "controversy conundrum." It is a very real problem. The more controversial your lectures, the more likely you are to receive lower student evaluations of faculty (SEF). Yet, teaching controversial issues is the essence of a university education.

There exist simple and well-known ways for a professor to avoid giving offense. One technique, when a class ostensibly focuses on a controversial subject matter, is to focus one's lectures on what other people have said. For example, a professor may, without raising any eyebrows, teach an entire course of lectures on ethics without ever making an ethical statement, since he confines himself to making reports of what other people have said about ethics. This ensures that no one can take offense towards him. During classroom discussions, he may simply nod and make non-committal remarks such as "Interesting" and "What do the rest of you think about that?", regardless of what the students say. (This provides the added "advantage" of reducing the need both for preparation before class and for effort during class, on the part of the professor.) Although pedagogic goals may often require correcting students or challenging their logic, SEF-based performance evaluations provide no incentive to do so, while the risk of reducing student happiness provides a strong incentive not to do so. Some students may take offense, or merely experience negative feelings, upon being corrected, whereas it is unlikely that students would experience such negative feelings as a result of a professor's failure to correct them. Overall, SEF reward professors who tell their students what they want to hear.

As far as I'm concerned, it's much more fun to tell students what they don't want to hear!

The article also makes a comment on the perception of students as consumers; and universities as businesses whose goal is to please the customer. Nothing could be further from the truth.

A fourth reason why SEF are widely used may be the belief that the university is a business and that the responsibility of any business is to satisfy the customer. Whether they measure teaching effectiveness or not, SEF are probably a highly accurate measure of student satisfaction (and the customer is always right, isn't he?). However, even if we agree to view the university as a business, the preceding line of thought rests upon a confusion about the product the university provides. Regardless of what they may themselves think at times, students do not come to college for entertainment; if they did, they might just as well watch MTV for four years and put that on their resumes. Students come to college for a diploma. A diploma is a certification by the institution that one has completed a course of study and thereby been college-educated. But that will mean nothing unless the college or university can maintain intellectual standards. A particular student may be happy to receive an easy A without having to work or learn much, but a college that makes a policy of providing such a product will find its diplomas decreasing in value.

Part of a university's responsibility may be to satisfy its students. But it is also a university's responsibility to educate those individuals whom it is certifying as educated. Unfortunately, those goals are often in conflict.

Here are some interesting comments from Professor Fich at the University of Toronto [Are Student Evaluations of Teaching Fair?].

Finally, I'd like to hear from you on the following point. Why are student evaluations anonymous? Shouldn't we be encouraging students to stand up and take responsibility for their opinions rather than hiding behind anonymity? Yes, I'm well aware of the fact that students think they will be punished for a negative evaluation. This is an unreasonable and illogical fear in most cases (i.e., at a respectable university). The point of a university education is to engage in debate and discussion. Trust me, most Professors can take it. Most students should start learning how to do the same.

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[Image Credit: The cartoon is from the ASSU Anti-Calendar]

Nobel Laureate: Richard Willstätter

 

The Nobel Prize in Chemistry 1915.

"for his researches on plant pigments, especially chlorophyll"



Richard Martin Willstätter (1872 - 1942) was awarded the Nobel Prize in Chemistry in 1915 for solving part of the structure of chlorophyll and the structures of some other plant pigments.

The presentation speech was delivered by Professor O. Hammarsten, Chairman of the Nobel Committee for Chemistry of the Royal Swedish Academy of Sciences.
THEME:

Nobel Laureates

By its property of making possible the assimilation of carbon dioxide under the influence of sunlight and hence introducing the synthesis of organic substances in the green parts of the plant, chlorophyll - as is well known possesses extraordinarily great biological significance and has an extremely important task to fulfil in the economy of Nature. The elucidation of the nature and the mode of operation of this substance is therefore a task which is of the highest degree of importance. The difficulties, however, which confront research scientists in this field have been so great that until very recently they have prevented a successful study of the problem of chlorophyll. Willstätter is the first, jointly with several of his students, to have been successful in overcoming these difficulties by working out new and very valuable methods and by extensive investigations carried out with masterly experimental skill. By the new and important discoveries resulting from these investigations he has been able to elucidate in all its essential parts the question of the chemical nature of chlorophyll.

It is true that earlier investigators had observed that chlorophyll contains magnesium, besides other mineral substances. Willstätter, however, has the merit of having been the first to recognize and to prove with complete evidence the fact that magnesium is not an impurity, but is an integral part of the native, pure chlorophyll - a fact of high importance from the biological point of view. He has shown that magnesium is held within the chlorophyll molecule in a manner which is very similar to the way in which iron is held in haemoglobin; this bond is so firm that the magnesium is not liberated even by the action of a strong alkali. On the other hand, it can be removed by an acid without injury to the remainder of the chlorophyll molecule, and the magnesium-free chlorophyll which can be obtained in this way is well suited to certain investigations. Willstätter has made use of this circumstance to test to what extent chlorophyll can be the same in different kinds of plants. Investigations carried out on more than 200 different plants, both phanerogamia and cryptogamia, showed that the chlorophyll was the same in all the kinds so far examined. This chlorophyll is, nevertheless, not a chemically homogeneous substance. It is a mixture of two somewhat different but yet closely related chlorophylls, one of them being blue-green, the other yellowgreen, and the former occurring more richly in the leaves than the latter.

The fact that chlorophyll in the ordinary sense is a mixture of two green pigments had, it is true, already been shown to be probable by Stokes in 1864, and both Tsvett and Marchlevski had brought forward important support for this view. It is Willstätter, however, who has here produced the certain and conclusive proof.

To prepare chlorophyll in an unchanged, pure state and in such large quantities that it can be the subject of complete chemical analysis has of course been one of the most important tasks of chlorophyll research; at the same time, it was one of the most difficult of all. By the successful solution of this task Willstätter has also been able to prepare the two above-mentioned different types of chlorophyll in a pure state and so supply exact proof of their existence. In doing so he has been able to carry out a thorough investigation of the large amount of the various derivatives which can be produced from these two different chlorophylls, and as a result of this means he has brought a desirable clarity and lucidity into a field of chlorophyll chemistry, which was previously very complicated and confused. By elaborating methods for the preparation of pure chlorophyll in rather large quantities he has also created new and rich possibilities for further fruitful research in this field.

The most important part of Willstätter's investigations is, nevertheless, that relating to the detection of the chemical structure of chlorophyll. He has shown that chlorophyll is an ester, which on saponification with alkali can be split up into a previously unknown alcohol called "phytol", which represents about one third of the molecule, and a colour component called "chlorophyllin", containing magnesium, which forms the remaining part. He has more closely investigated these two components both individually and for their transformation and decomposition products. Furthermore, he has found that this splitting-up of chlorophyll into the two mentioned main components can also take place as a result of the action of an enzyme occurring in the leaves, which he has called "chlorophyllase", and hence he has been able to elucidate the nature of the crystallized chlorophyll. He has established that this is not, as some investigators have assumed, the pure, unchanged natural pigment in the leaves. The crystallized chlorophyll is a laboratory product, an alkyl ester, which lacks phytol. The amorphous chlorophyll, containing phytol, is the unchanged natural pigment in the green parts of the plant.

A very important section of Willstätter's work on the chemical structure of chlorophyll is represented by his investigations into the colour components, the "chlorophyllin", and other "phyllins" and derivatives formed from it. These investigations are of particular interest with regard to the question of the relationship between blood pigment and chlorophyll.

From the iron-containing red blood pigment, haemoglobin, substances can be prepared, purple in colour and free from iron, which are known as porphyrins, and the one which has been known longest of these is haematoporphyrin. A substance very closely related to this, with regard to optical properties, has been prepared from a chlorophyll derivative by Hoppe-Seyler, who called this chlorophyll pigment phylloporphyrin on account of the similarity between the two substances. Schunck and Marchlevski have shown later that a chemical relationship does exist between blood pigment and chlorophyll, but in this case, too, it is Willstätter who has conducted the completely conclusive investigations.

In these investigations, which concerned the pigment nucleus both in chlorophyll and in haemoglobin, he has made several new and important observations regarding the pyrroles and their position in this nucleus; in particular, however, he has shown that from these two pigments the same parent porphyrin, "aetioporphyrin", can be prepared, whose molecule has retained the essential characteristics of the pigment nucleus. By doing this he has produced the most interesting and decisive proof of the relationship between the two most biologically important pigments in Nature - haemoglobin and chlorophyll.

He has also prepared in a pure state and studied exhaustively the yellow pigments, the so-called carotenoids, which occur together with chlorophyll in the leaves of plants. By means of the results obtained regarding both these yellow pigments and the chlorophylls he has paved the way for new biological researches into the part played by the different leaf pigments in the assimilation of carbonic acid.

He has also studied with great success another group of plant pigments, namely: the blue and red pigments of flowers, the so-called "anthocyanins". He has isolated the characteristic pigment and investigated its chemical nature from a rather large number of flowers, such as cornflower, roses, pelargonia, larkspur, hollyhock, etc., as well as from some fruits, such as bilberries, black grapes and cranberries. As a result, the anthocyanins have been shown to be glycosides, which can be split up into a kind of sugar - in most cases glucose - and a colour component, a "cyanidin". Willstätter has elucidated the chemical structure of these cyanidins; he has proved in what their difference consists in the various flowers or fruits, and has also proved their close relationship with the yellow pigments, occurring in Nature, of the flavone or flavonol group. By the reduction of one such yellow pigment, quercetin, he has obtained the cyanidin which occurs in roses and cornflowers, and by chemical synthesis he has succeeded in preparing the cyanidin of the pelargonia, pelargonidin. He has shown the dependence of the flower pigments upon the reaction of the plant sap and has thus explained how one and the same anthocyanin can have a different colour in different flowers, as is the case with roses and cornflowers. The anthocyanin is in both cases the same, but in the rose it is bound to a plant acid and is therefore red, whereas in the cornflower it is bound to an alkali and is therefore blue.

By extending his investigations to the yellow pigments of flowers as well, and by quantitative determination of the anthocyanins in certain kinds he has shown that the difference in the colour which the flowers assume in Nature or under the care of the grower depend upon several different circumstances, such as the appearance of several different anthocyanins in the same kind, great variations in anthocyanin content, different reaction of the cell sap and the simultaneous presence of different quantities of yellow pigments, which latter can again differ from one another in types.

In this field of plant-pigment chemistry, Willstätter's investigations can also be regarded as pioneering; the most comprehensive and the most important are, however, his investigations on chlorophyll, by which he has not only succeeded in unravelling the chemical structure of this substance, but also laid the sound scientific foundation for continued successful research into this extremely important field of plant chemistry.

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