Between the microscope and the naked eye : The lancelet seen larger than life (2008.8.1[Fri])

 

I think stereomicroscopes are kind of interesting in the way that they seem to bridge the capabilities of the eye and the standard optical microscope, magnifying images to just the right scale. Optical microscopes can allow one to see cells, while the unaided eye is not normally able to make them out. That's especially true for me now that my eyes are getting increasingly presbyopic, something I don't really want to think much about.

    Take a mouse or chicken embryo with the cartilage stained with Alcian blue, immerse it in a weak solution of about 30% glycerin, and have a look under a stereomicroscope, using a low resolution to start. What you'll see is magnified only a few times larger than what you could see with the naked eye, an extension of the familiar world of physical bodies of flesh and bone. Next, illuminate the specimen and gradually raise the magnification to its maximum, and you will just be able to make out cartilage cells appearing as translucent particles at the periphery of the cartilage and in areas undergoing ossification. Similarly, if you let a newly-hatched lamprey larva swim about in pure water against a black background, you can watch as cells fleck off from the tip of its tail, as the cadherin bonds disintegrate due to the lack of calcium ions. The white powdery stuff is the epithelial cells, falling away. If you want to view at even higher resolutions, you have to make the switch to an optical scope.

    Anatomy and morphology generally deal with the scales described above, while if you turn up the magnification a bit higher, you're looking at individual cells. In development processes as well, clusters of cells begin to appear at this same scale. The point being that the difference between the cellular and morphological levels is not that great. It goes without saying that morphological patterns are the culmination of phenomena that occur at the cellular level, so it wouldn't do to have too great a divide between the two scales, regardless of whether we understand the mechanisms that link them or not...

    If, for example, you use a marker to label the midbrain of a chicken embryo in day 2 of development, you can discern the first projection of the trigeminal nerve as it wends its way gutward. When I was first getting started in research, I would take photos of embryos and blow them up as big prints, then use that as an underlay and sketch peripheral nerves from morning till night, sometimes even going right down to the single-neuron level in detail. Looking back, I have to say I'm impressed that even back then I was trying to study embryology at the cellular level, but still coming from a gross anatomical context, which was pretty revolutionary at the time. I suppose I should have blown my horn a bit more loudly. I think that even now, observing things at this image resolution is an aid to the imagination when thinking about morphology at the cell or molecular level.

    I have previously written about illustrations so finely detailed as to be impossible to photocopy, so I thought I'd give one extreme example of that here. In July 1985, I left the Kyoto University Department of Zoology and took a position as a lecturer at the University of the Ryukyus Medical School in the anatomy department. It was there that I met the man who I consider my second true mentor, Shigenori Tanaka. One day Professor Tanaka advised me, "Don't make your illustrations too big." In those days, preparing manuscripts involved an arduous process of first drawing a painstaking sketch on A2 paper, inking it using laminated tracing paper of the same size, then using a Mamiya camera to take a hand-bill sized negative before developing it on thick photographic paper. So in a sense it we were already fully aware that making illustrations any larger than that size would be meaningless, and for a while I couldn't really understand why he kept muttering these warnings at me. Of course, if you draw an large image and then shrink it down, the resolution increases and it makes it look even more finely drawn than the original. So it might just be that he was counseling people not to be so foolish as to draw something that wouldn't fit onto the photographic mount.

    I figured this out the hard way around 1990, when I had returned to Japan after studying at the Medical College of Georgia in the US. I came across some sketches of the amphioxus vascular system left by Ryoji Ura, who had already passed away by that time. I mentioned before a series of articles on the development of the vascular system, and Dr. Ura was none other than the author of these. Professor Tanaka was his student, which I suppose makes me the next in that lineage, something like his academic grandchild. The sketches were shown to me by another of his "grandsons," Reiji Hirakou (the supervising translator of Romer and Parson's "The Vertebrate Body"), so it would not be surprising at all if my erstwhile mentor Prof. Tanaka was already familiar with them. And just what were these sketches?

    Each image was the length of about a tatami mat (about 1.7 meters), showing the adult lancelet vascular system outlined in ink in gigantic detail, with each blood vessel rendered in lines so fine they seemed to have been drawn with a mapping pen. What's more, the work remained unfinished. Or should I say, it wasn't clear to me whether it would be possible to complete such an undertaking, or how it could ever be considered to be finished. Mapping pens can be used even by amateurs and produce some of the finest lines of any pen type. Now try to imagine the full complement of blood vessels in the adult amphioxus as they fork, anastomose and form networks rendered in the finest conceivable lines on a mat-sized canvas, and you'll have an idea of the sheer scale of the project. It was so detailed that depictions of individual endothelial cells would not have seemed out of place. I think my pupils and lenses must have been screaming at the effort to take it all in. I doubt the means for reproducing such an image intact at its original scale exists. Even if you were to, for example, scan it in its entirety as a JPEG and then scroll through it on a monitor section by section, you couldn't really say you'd "seen" it, in my opinion. I also doubt it was the only such sketch by Dr. Ura. So I think what Prof. Tanaka was communicating was a mixture of admiration and dismay for such beautiful works of anatomical art that could only exist as originals. For my part, now that I spend so much of my time looking at originals, I can't help thinking that was actually the lament of Dr. Tanaka.

    In nineteenth century France, there were enormous natural history volumes, known as elephant folios, that were more than half a meter in length. Kiener's Species General et Iconographie des Coquillages Vivantes is one such example. The only chance for anatomical illustrations such as Ura's to find a publisher may have been in the France of yesteryear. Of course, even if it had been published at elephant size, it would have needed to be bound in... The use of copperplate printing and lithography using minute lineaments and colored with watercolor paints to portray nature in the greatest detail possible is certainly in line with the obsessive spirit of natural history, making it that much easier to believe the tales of practitioners who went blind in pursuing their art. In addition to being one of the great Japanese scholars of anatomy, Dr. Ura was without doubt one of the keepers of that spirit as an artist as well.