248 THE PRESENT EVOLUTION OF MAN — PHYSICAL 



a diseased mother will exhibit a like immunity. Here 

 the toxins, soluble substances, passing, even when 

 there is no breach of continuity in the vessel walls, 

 from the diseased to the healthy individual, cause a 

 reaction in the phagocytes of the latter by virtue of 

 which they are enabled, if the microbes at any future 

 time find entrance, to destroy them. 



So also as regards other zymotic diseases, small-pox, 

 measles, &c., against which immunity may be acquired ; 

 while it is certain that a parent who has acquired 

 immunity does not confer it on the offspring which 

 subsequently arise from his or her germs, it may safely 

 be prophesied, though I am not aware that the 

 phenomenon has actually been observed, that a pregnant 

 mother, suffering from any such disease, if she recovers 

 and does not abort, will confer immunity on her foetus of 

 as enduring a nature as it would acquire did it take the 

 disease itself after birth and recover. Mr. Hutchinson 

 speaks of immunity acquired in this way as an unexpected 

 fact ; I think, however, we may claim that the fact is 

 just such as might be expected. The only thing 

 puzzling about the process is the circumstance that an 

 individual, in whom the toxins alone are present, 

 acquires immunity so much more quickly, and with so 

 much less injury, than an individual in whom the 

 microbes are present as well as the toxins ; for instance, 

 a non-infected mother, pregnant of a syphilitic embryo, 

 acquires immunity with far greater speed, and with far 

 less harm to herself, than a woman who is actually 

 infected, and in whom the microbes are present as well 

 as the toxins. The explanation of this is probably 

 found when we remember the great length of the 

 incubation period, and of the general duration of the 

 disease. This seems to imply that the toxins of 

 syphilis are of feeble virulence, a conclusion which is 

 further borne out by the circumstance that the general 



