246 THE PRESENT EVOLUTION OF MAN — PHYSICAL 



Unfavourable conditions merely constitute the battle- 

 field, the microbe is the bullet that wounds. " It is not 

 the disease tuberculosis that comes into the world with 

 certain individuals, or with successive children of the 

 same family, but the aptitude to contract it should ex- 

 ternal conditions favour." — Prudden. The consumptive 

 diathesis, if by that is understood comparatively feeble 

 powers of resisting the tubercle bacilli, may be either of 

 the inborn kind or of the acquired kind, or it may be a 

 compound of both. That only the inborn kind, or only 

 that part which is inborn of a diathesis compounded of 

 both kinds, is transmissible, is decisively proved by the 

 fact already dwelt on at length, that races that have 

 long and severely been afflicted by tuberculosis are 

 more resistant to it than races which have not been so 

 afflicted. 



More than any other disease syphilis has furnished 

 arguments to the supporters of the Lamarkian theory. 

 The microbe producing it is apparently so minute, and 

 of such little virulence, that alone of all pathogenic 

 organisms it is able to take up its abode in or on the 

 spermatozoon without destroying it, and so to accom- 

 pany the latter in its long and devious journey to the 

 ovum ; for thus only is explainable the well-known fact 

 that a healthy mother may bear a syphilitic child to an 

 infected father. On the other hand, parents, both of 

 Avhom are infected, may have for offspring a healthy 

 child, as in the case mentioned by Mr. Jonathan Hutch- 

 inson {Syphilis, p. 412), when of twins born to parents 

 both of whom were suffering from the disease in a viru- 

 lent stage, one twin was diseased and the other healthy. 

 Here, as regards the healthy child, not only cannot the 

 spermatozoon have received and conveyed infection, but 

 the ovum as well as the developing embryo must have 

 escaped it, a combination of events which must neces- 

 sarily be rare. The limiting membranes of the ovum 



