130 THE PRINCIPLES OF HEREDITY 



differentiation of tissue for the performance of different 

 functions; in them therefore there are no cells which can 

 react to the toxins ; and therefore neither ovum nor sperm- 

 atozoon has the power of resisting the parasites, or, in other 

 words, of acquiring immunity. This power, like the power of 

 acquiring all other use-acquirements arises much later in 

 their cell-descendants, when these have undergone morpho- 

 logical and physiological specialization and differentiation into 

 skin, muscle, gland, nerve, phagocyte, and other cells. Hence 

 it follows that a man can never confer immunity on his 

 children; for though his spermatozoa be steeped in toxins 

 they cannot react, since the necessary machinery is wanting. 

 So also, a woman, who has recovered from syphilis or any 

 other disease, cannot then confer immunity on her non -infected 

 children ; for, though during her illness her ova are steeped 

 in toxins, yet in them also the machinery for reaction is 

 wanting. But if a woman become pregnant during her ill- 

 ness, then in her foetus, if it be not too immature, there are 

 present differentiated and specialized cells, which like those 

 of her own body have the power of acquiring various traits, 

 among others the power of reacting to the toxins of this or 

 that disease. And, therefore, while a man can never confer 

 immunity on his children or a woman on children born to her 

 before infection or after recovery (unless they be themselves 

 infected), a woman can confer immunity on offspring of 

 which she is pregnant during her illness, for in the latter 

 case the machinery for acquiring immunity is present that 

 is, the toxins passing from the mother to the embryo, may 

 produce a protective reaction in the cells of the latter, 

 especially those concerned in the elaboration of the digestive 

 bodies. 



208. But syphilis is a disease of long duration ; in other 

 words, immunity against it is only very slowly acquired ; the 

 cells only very slowly acquire the power of tolerating the 

 toxins, and of producing the digestive bodies undeterred by 

 their presence. It follows that if a woman become pregnant 

 during the earlier stage of her illness, even if the microbes 

 be stopped in the placenta and the child is not infected, there 

 will pass from her to the embryo toxins which are little if at 

 all attenuated ; and, therefore, since young individuals are, in 

 general, less capable of resisting zymotic diseases than the 

 older members of their species, the embryo perishes, and the 

 mother aborts or miscarries. But as her disease progresses 

 the mother gradually acquires more resisting power ; her cells 

 become more and more tolerant of the toxins, and, therefore, 



