128 THE PRINCIPLES OF HEREDITY 



menon the healthy individual is found to be immune to the 

 disease ; for such an infant does not acquire the disease when 

 suckled by his infected mother, nor, on the other hand, as 

 Colles proved, does such a healthy mother contract the 

 disease when suckling her infected child, though other non- 

 infected women may. Here, during gestation, toxins passing 

 from the infected to the non-infected individual inure the 

 cells of the latter to resistance, as a result of which they 

 destroy the micro-organisms if at any future time, in the 

 act of sucking or giving suck, they find entrance. But 

 children born of a mother who has recovered from syphilis, 

 and who is immune, are not themselves immune like the 

 healthy children born to her during her illness. Whence it 

 follows that her continued immunity is not due to the 

 presence of chemical antidotes or digestive bodies; for if it 

 were her offspring would continue to be born immune, just 

 as they did (if not infected) when she was ill. Her continued 

 immunity, therefore, is plainly due to the fact that her cells 

 do not lapse the training they received when she was 

 suffering from the disease. 



206. In connection with syphilis it would be interesting to 

 seek the explanation of some instructive phenomena which 

 occur in the inherited form of that disease. If a man 

 contract syphilis, then, after a certain number of years, of 

 which the limit has been set at five, he ceases as a rule to be 

 infective to a woman, but for very long after he may have 

 offspring who exhibit the signs of very virulent infection. If 

 a woman contract syphilis, then, like a man, she also ceases 

 after a limited time to be infective to another adult, and not 

 only this, but, unlike the man, she ceases also to be infective 

 to her children (Diday's law of decrease). A woman's power of 

 infecting her children is, therefore, of a much shorter duration 

 than that of a man. Speaking only in general terms and 

 without regard to the numerous exceptions, which doubtless 

 depend on variations in resisting power in the offspring, the 

 children earliest born to her after infection suffer, in the 

 absence of treatment, most severely from the disease ; those 

 later born less severely ; till, at length, if she continue to bear 

 children, the latest born do not suffer at all. Her disease 

 tends at first to result in abortions and miscarriages ; then in 

 the birth at term of one or more dead children ; then in one 

 or more children who survive birth for a space; next in 

 children who survive, but show signs of disease ; and lastly 

 in children who show no sign of infection. If such a woman 

 mate with an infected man, this law still holds, for which 



