390 THE GERM-PLASM 



of susceptibility. A large number of facts seem to me, on the 

 contrary', to support the view that infection of the germ plays 

 the chief part in tlie process. It would be out of place to enter 

 into particulars and attempt to prove this view here — the question 

 belongs to the province of the pathologist : 1 merely wished to 

 point out in this connection that a combination of hereditary 

 transmission and infection of the germ is perfectly conceivable. 

 The phyletic origin of such constitutional diseases is presumably 

 to be explained as being due to the occurrence of certain in- 

 dividuals possessing constitutions which were abnormally sus- 

 ceptible to a certain kind of microbe. Such persons would be 

 more readily attacked from without by this particular disease. 

 If, however, it once attacked them, and were it of such a kind 

 as to cause death only after some time, a further and much 

 surer opportunity was offered to the microbes for transferring 

 themselves to other hosts than was previously the case when 

 they passed into the body from without : — they settled in the 

 germ-cells of the individual affected, and were thus transferred 

 to the descendants of this individual. Although the presence 

 of parasites in the germ-cells has not yet actually been proved 

 in the case of tuberculosis, in my opinion it by no means follows 

 that such an infection does not nevertheless take place : we do 

 not even know whether such microbes are of the ordinary 

 form and size. In any case they must possess different vital 

 qualities ; for did they multiply in the tgg- or sperm-cell in 

 the same manner as in the tissues in which they are known 

 to occur, the germ-cells would soon be destroyed. Numerous 

 adaptations to the host may have occurred in this case as in 

 that of other parasites ; and, moreover, latent periods of develop- 

 ment may have arisen during which the parasite does not 

 undergo multiplication. It seems improbable that such arrange- 

 ments should not be met with, and that the parasite should not 

 make use of the favorable opportunity of becoming distributed 

 with the greatest certainty. Latent periods very commonly 

 occur in the germs of animals and plants whenever they are 

 useful, and hence this arrangement must come about without any 

 great difficulty. 



Even although our most eminent pathologists, such as Ernst 

 Ziegler, are now of opinion that tuberculosis is not transmitted 

 by infection of the germ, because such a transmission has not 

 been directly proved, and because, on the other hand, an in- 



