Page:George Archdall Reid 1896 The present evolution of man.djvu/259

and spermatozoon probably prevented tbe entrance of the pathogenic microbes, which, judging from the observed behaviour of the micro-organisms of many other diseases, probably find their nutriment normally in the -fluids of the host, and are taken up by certain cells, the phagocytes, only when an attempt is made to destroy them. The escape of the embryo is more easy to understand. As has long been known, there is no connection between the blood-vessels of the mother and those of the foetus, and therefore no blood flows from the one set of vessels into the other. They are, however, in intimate apposition, and are so thin-walled that, while no solids can pass from the parent to the embryo, or vice versâ, fluids with absorbed gases pass readily by osmosis. Like other solids, the microbes of disease are stayed in the placenta,—Klein mentions that he has examined the placenta of a guinea-pig dead of anthrax, and found the microbes therein strictly limited to the maternal part of it,—and cannot, therefore, under normal circumstances infect a healthy embryo from a diseased mother, nor vice versâ. Under abnormal circumstances, which may be induced by the action of the micro-organisms themselves, a breach of continuity in the walls of one or more vessels occurs, and the micro-organisms pass from the diseased to the healthy individual. In cases when this does not happen, when a healthy child is born to a diseased mother, or when a healthy mother bears an infected child to a diseased father, it is highly significant that the healthy individual is henceforward, or for a considerable time, immune to the disease; or at least a healthy mother who has borne an infected child is immune to the disease, as is proved by the fact that she does not contract it when giving suck to her infant, whereas other healthy women become infected if they similarly tend it; and it may safely be prophesied that the healthy child of