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

BOOK 3 THE SCIENCE OF LIFE

CHAPTER 3

eye that can pierce below the surface ; for, about acentral theme which is never forsaken, . as T. H. Huxley wrote, “ Flowers are the however it may, momentarily, cease to be primers of the morphologist ; those who apparent.” Only descent seems able to

Fig. 132. The fore-limbs of three flying vertebrates, showing different modifications of the same structural plan. Above, a Pterodactyl. The wing-membrane is stretched on the enormous “Tittle”? finger, three other fingers are left as claws. In the centre, a Bat. Only the thumb is left as a claw ; the other four fingers are used to spread the wing on. Below, a Bird. The thumb is a mere vestige, and besides this only the second and third digits remain.

explain that unity.

Of recent years fresh support for the evolutionary idea has been forthcoming from a new quarter in the proof of the chemical resemblances and differences between animals and plants. This is really evidence of the same kind which we have just been examining, save that the witness speaks a different language. The evidence still concerns resemblances in construction, but they are the invisible resemblances of chemical structure instead of the visible ones of anatomy.

Let us be a little more explicit about this new line of evidence. Many of the triumphs of modern medicine, as the reader probably knows, such as the antitoxin treatment of diphtheria, or preventive inoculation against typhoid and paratyphoid fevers, are based upon the fundamental principle that when any foreign substance belonging to the chemical group of proteins gets into the circulation, the body manufactures an “antibody > —a substance which in some way neutralizes the foreign protein or puts it out of action; and the antibody acts with full force only against the particular protein introduced, with less force against proteins of similar chemical

run may read in them uniformity of type structure, and not at all against the rest. amidst endless diversity of plan with com- Now, one of the chief ways 1n which the

plex multiplicity of detail. As a musician foreign protein may might say, every natural group of flower- by precipitating it in solid form.

be put out of action is Tf, for

ing plants is a sort of visible fugue, wandering example, a rabbit be poisoned by a few

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