2OO 



Of the remaining infectious diseases which are also purely 

 contagious I have yet to consider glanders, malignant pustule, 

 rabies, virulent ulcers and blennorrhceas, pyaemia, and puer- 

 peral fever ; these, however, being all caused by external 

 poisons introduced into the system, need not detain me here, 

 as heredity can have nothing to do with them beyond the 

 fact that the system into which they are introduced may have 

 an inherited constitutional peculiarity which will predispose 

 to their influence. Indeed, of this there can be no doubt, 

 as none of them can germinate without a suitable soil, and 

 in the case of each one of these affections, many individuals 

 seem to be especially predisposed, while others show com- 

 parative immunity. I may now briefly sum up the results of 

 our inquiry as to whether the acute infectious diseases are 

 subject to heredity, and if so, to what extent. I have asserted 

 that so far at least as the exanthemata are concerned, the 

 mental and physical condition of affected individuals may 

 remain unaltered, after the attack has subsided. Their 

 tissues, however, will be so far altered as to be able in all 

 probability to withstand a second attack of the same poison 

 during their lives. This immunity, however, is probably 

 seldom complete, and never universal. Thus these affections 

 leave no taint to be transmitted. On the other hand a 

 predisposition, or insusceptibility, is very frequently mani- 

 fested by those exposed to the influence of these specific 

 poisons, and here heredity has been a most important agent, 

 with the exception of those cases in which a predisposition 

 may have been acquired by repeated attacks (as in the case 

 of erysipelas and diphtheria), or in which insusceptibility 

 represents the immunity resulting from a first attack. 



Although a chronic, and not an acute infectious disease, I 

 may here allude to syphilis, as it is so markedly contagious ; 



