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

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THE EVIDENCE FROM PLANT AND ANIMAL STRUCTURE

Fig. 133: Above: A Moth (Poplar Hawk Moth) ; a Locust ; a Flea.

Six insect faces.

Below : A House-fly, sucking a drop of liquid ; an Ant ;

e aomale aera Mosquito, with the parts of its proboscis separated. The mouth-parts, whether built for sucking, licking, Ci ens iting, or frercing, are all built on the same general plan—unpaired upper lip and three pairs of jaw-appendages. e last two pairs usually bear little feelers or palps, as shown in the locust ; one pair of these is seen in moth and fly.

Injections of horse’s blood it produces an antibody which gives its own blood the power of precipitating the blood of horses. If measured quantities of the bloods of treated rabbit and of a horse be mixed in a test-tube, a cloud appears and settles to the bottom—the horse-proteins have been eliminated.

If, however, the same amount of the treated rabbit’s blood had been mixed with blood from a hen, there would have been no precipitate, not even a trace of cloudiness. The rabbit antibody which was efficacious with horse-proteins would be totally ineffective with hen-proteins. But if it had been mixed with donkey’s blood, there would have been a precipitate—only not quite so much as if horse’s blood had been used; while cow’s or sheep’s blood would have given a definite, but very much smaller precipitate. It is obvious from general structural considerations that a donkey is more nearly related to a horse than a cow, or a cow thana hen. Here we find that this relationship extends to the chemistry of the proteins. In brief, after animal X (a rabbit is generally used for this purpose) has been treated with the blood

of a second kind of animal A, then the amount of precipitate which its blood gives with the blood of A and of other kinds of animals B, C, D, is found to be proportional, so to speak, to the closeness of relationship of these latter to A, as measured by anatomical likeness) A great amount of work has been done on this subject, much of it summarized in Nuttall’s book, Blood-Immunity and Blood-relationship, and it is of great technical interest.

Wherever the evidence from comparative anatomy is clear, this new chemical evidence is in agreement with it. The anatomist, for instance, tells us that seals and sea-lions are carnivores which have taken to life in the sea ; and their blood-proteins are chemically more like that of dogs, cats, and bears than of any other creatures. The anatomist puts man in the same group with the apes and monkeys, and tells us that he is more like apes than tailed monkeys, more like tailed monkeys than lemurs, and more like any of these than he is to all the rest of the mammals. His very blood-proteins reinforce this conclusion. The blood of a rabbit previously inoculated with human blood gives a heavy precipitate when tested with

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