The science of life : fully illustrated in tone and line and including many diagrams

BOOK 2

There is a possibility—a hotly contested possibility—that an epidemic destruction of bacteria themselves that sometimes breaks out in cultures is due to a living thing called bacteriophage (or devourer of bacteria), which, if it exists at all, is about a fiftieth of a micron across.

This, we may note, is getting within measurable distance of the sizes of the ultimate units of which living things are made up. A single molecule of protein is somewhere about a thousandth of a micron across, so the body of a single bacteriophage organism cannot contain much more than a thousand protein molecules. But the living nature of bacteriophage is still a matter of controversy. We may note that all the ultramicroscopic organisms whose existence has been proved are causers of diseases, and this is but natural; the pain they cause has spurred us to their discovery. It is perfectly possible that there are other kinds living independently in the soil, for example, just as visible bacteria teem everywhere (although the tentative search that has already been made has as yet revealed none). It may be that there is a world of these incredibly minute forms of life, as little suspected as was the world of microbes three hundred years ago.

A tantalizing situation! Broad hints of the existence of these creatures, even proof in some cases, and yet no instrument to see them with! But happily a new method is being worked out, a method by which we can pry into the anatomy of some at least of the larger of these ultramicroscopic creatures. It has been shown that although we cannot see them with any distinctness we can take their photographs.

So recently as 1925, Mr. J. E. Barnard devised a method, demanding the most elaborate apparatus and an infinity of patience and experimental skill, by which we can extend our knowledge a little farther. It rests on the fact that ultra-violet light has a shorter wave-length than visible light, therefore if objects are illuminated under the microscope with ultra-violet light their images will show finer detail than is possible with visible light. Now ultra-violet light has no action on the retina, so these images cannot be seen; nevertheless, it blackens a negative, so they can be photographed. ‘The first organisms to be examined in this way were those that cause a disease of the lungs in cattle. The result was surprising. ‘The organisms were found to be not miniature bacteria but creatures as different from bacteria as bacteria are from protozoa or

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THE SCIENCE OF LIFE

CHAPTER 6

moulds. Bit by bit, by photographing cultures in different stages of growth, the story of their life-cycle was pieced together.

In the first stage in the cycle, the stage that escapes direct observation and passes through filters, the creature is a very minute particle, about one-fifth of a micron across. Apparently these particles can proliferate directly. But they also have a method of multiplication utterly unlike that seen in bacteria. They swell up into hollow spheres, six or seven times as large—big enough to be seen with a microscope; then little wart-like thickenings appear dotted over the walls of the spheres and detach themselves. ‘These are the particles with which we started. Sometimes the particles remain connected for a time to the parent sphere by means of an incredibly fine thread before they break away. Sometimes a number of particles and spheres may be found thus connected together. And that is pretty nearly all we know. It is a fascinating story because the creatures are so unlike anything that has yet been seen, and fascinating also because it is incomplete, the first step in what must become a profoundly important branch of investigation.

A second step also has been taken: Barnard has photographed similar but even smaller organisms—about a tenth of a micron across—from certain types of cancerous growths of fowls and of men. But whether these organisms are the cause of cancer is a matter that we shall discuss in a later Book. Tt will be noticed that the creatures which have been photographed in this way are only just beyond the margin of visibility ; how far it will be possible to develop the method and reveal yet smaller organisms it is difficult to say. Acorner of the veil that hides these tiny creatures has been raised for an instant, an instant long enough for the click of a camera ; the rest, at present, is darkness.

And so, on a note of uncertainty, we close our account of the known forms of life. There are living things, as we have found, that are out of reach of microscopes, at least when we use ordinary light; they are almost entirely mysterious as far as our present-day knowledge is concerned. How far we shall be able to investigate them depends on the methods that we are able to devise. ‘There is no need for us to despair. Bragg, by passing X-rays through crystals, has been able to find out how their very atoms are arranged—it is as if he could see them. It may be that the biologists also will arrive at roundabout but nevertheless reliable ways of exploring the anatomy and physiology of these specks of life and so ‘* by indirections find directions out.”