The physics of kitteh drinking

November 11, 2010 • 11:56 pm

by Greg Mayer (update below)

Pedro Reis of MIT and colleagues are about to publish a paper in Science analyzing high speed films of cats drinking. A preprint is already available. I’m not sure there’s really anything interesting here, other than cool video. You can tell that only the tip of the cat’s tongue contacts the milk, so the ‘brushy’ part of the cat’s tongue is not involved in getting milk into the mouth, which is not what I would have expected. (The brush has a large surface area, which I thought would be involved in liquid adhesion, but it’s not.)

There are more videos at Reis’s website, here and here. Ed Yong at Not Exactly Rocket Science has more background on the work, and notes that MIT’s Harold ‘Doc’ Edgerton (of Loch Ness monster fame) made high speed film of cat lapping in 1940. The cat is at about 4:41.

Edgerton (or at least his film’s narrator) thought the back of the tongue cupped the milk, but Reis’s better films show the milk is on the front of the tongue, not the back, curled part of the tongue. The BBC also has a story up.

P.M. Reis, S. Jung, J. Aristoff and R. Stocker. 2010. How Cats Lap: Water uptake by Felis catus. Science in press.

Update. MIT has a press release with more background available here. I mentioned that cats don’t ladle the milk, nor is it the brushy part, and I’ve been queried about what it is they do do. Here’s how the MIT press release puts it:

Cats, unlike dogs, don’t dip their tongues into the liquid like ladles. The cat’s lapping mechanism is far more subtle and elegant. The smooth tip of the tongue barely touches the surface of the liquid before the cat draws its tongue back up. As it does so, a column of liquid forms between the moving tongue and the liquid’s surface. The cat then closes its mouth, pinching off the top of the column for a nice drink, while keeping its chin dry.

When the cat’s tongue touches the liquid surface, some of the liquid sticks to it through liquid adhesion, much as water adheres to a human palm when it touches the surface of a pool. But the cat draws its tongue back up so rapidly that for a fraction of a second, inertia — the tendency of the moving liquid to continue following the tongue — overcomes gravity, which is pulling the liquid back down toward the bowl.

The release goes on to mention that the cat instinctively knows when to close its mouth, but the paper did not in fact address that question, and cats may well learn the timing (much as first basemen learn the perfect time to snap their glove shut). The NY Times has a story up now too. Besides the cool video, the most interesting thing to me about the paper is that they were able to predict a relationship between lapping frequency and body mass, and show that their prediction roughly held (see Fig 4c of the paper; the authors  make only a glancing reference in the text).

A lunch for the speakers

November 11, 2010 • 6:31 am

The Colombians know how to put on the dog when it comes to feeding scientific visitors. Here’s the lunch we had yesterday (others have been just as good).

Apéritif: a jugo, green mango juice heavily infused with ginger. Spectacular!

Appetizer: Tropical fruit cup

Main course:  ajiaco, a traditional chicken/potato soup from Bogotá.  It comes with lots of mix-ins: capers, cream, hot sauce, parsley, rice, banana, avocado, and a disk of arepa, the Colombian equivalent of a tortilla.

Before doctoring:

After doctoring; this was one terrific meal:

Finally, postre: ripe sauteed plantains with a caramelly sauce.

There was also wine on offer, but why would anybody want booze when you can drink freshly-squeezed tropical fruit juice?

Many thanks to the organizers of this meeting, particularly Dr. Angela Restrepo, for running a fine symposium and providing terrific amenities. There is sightseeing today, and I’m off to Bogotá tomorrow.

Science goes to Hollywood– favorite movie scenes, 1

November 11, 2010 • 12:10 am

by Greg Mayer

Continuing our consideration of  science in the movies, here’s the first of my selections. It’s from 1959’s Journey to the Center of the Earth, starring James Mason as the uber-spelunker Prof. Oliver Lindenbrook, who, in the scene beginning at 1:55, has just returned to Edinburgh from the center of the Earth. (This is, by the way, how my typical undergraduate lecture begins– I am led in by colorfully-garbed, mace-wielding administrators, while hundreds of formally dressed students chant my name, demanding that I speak. Later, of course, they sing songs in my honor, acclaiming me “master of all natural history”.)

Lindenbrook’s key statement is:

“If they are meant as praise for a successful scientist, I must disclaim that honor. No, a scientist  who cannot prove what he has accomplished has accomplished nothing. I have no records, no shred of evidence; I will never embarrass this distinguished university by asking that it take my word.”

I show this clip to my class on science and pseudoscience, a general education class on such things as UFOs, cold reading, creationism, and cryptozoology. It expresses very nicely something I stress in the class: that scientific claims are based on publicly available evidence. Having lost his notes, his specimens, and his artifacts during his escape from the center of the Earth via a volcano, Lindenbrook has nothing but his recollections, and this is mere testimony, an anecdote– nothing he can show to fellow scientists to examine for themselves. He does not have scientific evidence; and as the Royal Society puts it, nullius in verba. The one off-note here is the use of the word “prove”: colloquially this may be acceptable, and scientists do use it, but, strictly, proof is something reserved to logic and mathematics, not the empirical sciences.

Besides this, my favorite scene, I like the movie as a whole as well, although its scientific content is not especially plausible ( giant reptiles living on the shore of a sea inside a lighted cavern at the Earth’s center?). There are some wonderfully semi-cheesy early special effects: lizards with sails attached to their backs to make them look like Dimetrodons, for example. (The lizards, by the way were not ordinary green iguanas, but rare West Indian rock iguanas, Cyclura.) But the scene above captures a real and important aspect of science. In my own specialty of zoogeography, I’ve had debates with colleagues about where particular species of animals are found; but we all know that “take my word for it” just doesn’t cut it.

Among the readers’ favorites in the comments on the previous movie science post, there have been a number of  interesting suggestions, some new to me, but also including some of my other favorites, like Contact and War of the Worlds. I’ll try to say more about these in a later post. In the meantime, keep commenting on your favorites.

Medellín, Colombia

November 10, 2010 • 7:36 pm

Filling up a valley in the Andean foothills, Medellín is a sprawling but attractive town with a tortuous history. Famous to Americans as the home of the Medellín drug cartel in the 90s, and once racked by political instability and guerilla warfare, the city has taken great strides to tamp down crime (cops and soldiers are everywhere) and to even out the terrible economic inequalities that sunder this society.

Science goes to Hollywood– what are your favorites?

November 10, 2010 • 4:19 pm

by Greg Mayer

Jerry recently posted on a piece by Carl Zimmer on the depiction of science in movies. Carl doesn’t think Hollywood films have shown very realistic views of science and scientists, and is not sure Hollywood can or should do anything about it. Carl’s more jazzed by the promise and accomplishments of smaller films of the type shown at the Imagine Science Film Festival. This got me to thinking about my own favorite science-y movies, and so, in the spirit of Jerry’s recent literary selections, I thought I’d mention some of my favorite depictions of science and scientists on film. I’ll be putting one up each of the next few days.

I invite WEIT readers to tell us in the comments what are their favorite scenes or films. The ones I’m thinking of capture something I believe to be true about the scientific enterprise; let us know what you found appealing in your favorite. It might be a kernel of truth, but it might be a ‘so bad it’s good’ (a la Plan 9 From Outer Space) kind of thing. I’ll put my first one up tomorrow.

(As an aside, I note Carl wondered why the acid in Alien didn’t burn through the hull of the Nostromo; much more fantastic is how the alien managed to put on about 500 kilos and grow ten feet longer without eating anything after emerging from John Hurt’s chest. The acid, after all, would be used up in the course of reacting with the metal in the hull, but where’d all that body mass come from?)

 

Things we never knew: maggots are covered with eyes!

November 10, 2010 • 3:53 pm

by Matthew Cobb

[First posted over at z-letter.com]

I work with maggots. Not big fat maggots you use for fishing, but Drosophila maggots. They are incredibly simple, but are capable of performing most of the behaviours shown by the adult fly (with the obvious exceptions of mating and flying). The tiny flyDrosophila was chosen by Thomas Hunt Morgan at the beginning of the last century when he decided to study evolution. After a few years, his attempt to make Drosophilaevolve was coming to nothing, when he found a white-eyed mutant fly. The rest, as they say, is history, as Morgan and his students revealed the laws of genetics that had been sketched out half a century earlier by Mendel.

Throughout the 20th century, Drosophila was studied by geneticists, and it was the first multicellular organism to have its genome sequenced, just as the new millenium dawned. Now there are hundreds of laboratories around the world studying the genetics and neurobiology of Drosophila. It would be fair enough to imagine that we knew almost everything there is to know about which cells do what in the fly, and even more so in its juvenile, more simple form, the maggot. How wrong that would be!

An article soon to be published by Nature from the world-famous laboratory of Lily and Yuh Jan describes the astonishing finding that Drosophila maggots – and, you can be pretty sure, virtually every other kind of fly maggot – is covered with tiny “eyes”. Nobody had any idea that this was the case.

Up until today, the maggot’s “eyes” were thought to be a group of 12 cells called Bolwig’s organ. They are named after the Danish scientist Niels Bolwig, who did his doctoral thesis on vision in fly maggots, and later went on to pioneer studies of primates in the wild; he died in 2004. There are two Bolwig’s organs, which you might imagine are the dome-shaped things on the front of the maggot’s face below. These structures are in fact the maggot’s “nose” or dorsal organ (my favourite bit of a maggot).

Bolwig’s organs, as shown in this lovely image by Bala Iyengar, are not at the front of the face, but instead deep inside the maggot’s body:

The Jan lab show that if the Bolwig’s organs are killed, maggots would still avoid light – (b) below – just like normal maggots (a) below:

There’s a great video on the Nature website showing a Bolwig-less maggot squiggling away from the light.

This proves that there must be some other cells in the maggot that can detect light (there was no change in temperature when the maggots had a light shone on them). Furthermore, Bolwig-less maggots did not respond to green or red light, but did avoid short-wavelength light at high intensities.

The paper reports that a particular set of cells in the maggot’s body wall, called class IV dendritic arborization neurons, responded to light – even when they were grown, isolated, in culture. These cells cover the whole of the maggot, as seen in this dramatic image – all the green cells are class IV neurons, and every one is an “eye”!

Amazingly, it turns out that these cells also express a taste receptor, Gr28b, which may be directly involved in sensing light, although this has yet to be demonstrated. This isn’t quite so surprising in that in the nematode worm C. elegans, a similar gene is also involved in responses to light. Another protein, TrpA1, which is involved in responses to light in the adult fly, is necessary for these class IV neurons to respond.

The authors conclude:

Our study has uncovered unexpected light-sensing machinery, which could be critical for foraging larvae to avoid harmful sunlight, desiccation and predation. By providing precedence for photoreceptors strategically placed away from the eyes, our finding of an array of class IV dendritic arborization neurons with elaborate dendrites tiling the entire body wall, and acting as light-sensing antennae, raises the question of whether other animals with eyes might also possess extra-ocular photoreceptors for more thorough light detection and behavioural response.

Even more importantly, this surprising result shows quite how much we have yet to discover about this animal about which, many people might have thought, we knew virtually everything. We know so much, but so little!

Yang Xiang, Quan Yuan, Nina Vogt, Loren L. Looger, Lily Yeh Jan & Yuh Nung Jan (2010). Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall.Nature. doi:10.1038/nature09576