THE LIVING MACHINE BUILDING FACTORS. 185 



minal substance. Indeed, it is not easy to see 

 how any external conditions can have influence 

 upon this germinal material if it is not an active 

 part of the body, but is simply stored within it 

 for future use in reproduction. How could any 

 changes in the environment of the individual 

 have any effect upon this dormant material 

 stored within it? But if we are correct in 

 regarding this germ material in the reproductive 

 bodies as the basis of heredity and the guiding 

 force in development, then it follows that the 

 only way in which congenital variations can 

 occur is by some variations in the germ plasm. 

 If a child developed from germ plasm identical 

 with that from which its parents developed, it 

 would inherit identical characters ; and if there 

 are any congenital variations from its parents, 

 they must be due to some variations in the germ 

 plasm. In other words, in order to explain con- 

 genital variations we must account for variations 

 in the germ plasm. 



Now, there are two methods by which we may 

 suppose that these variations in the germ may 

 arise. The first is by the direct influence upon 

 the germ plasm of certain unknown external 

 conditions. The life substance of organisms is 

 always very unstable, and, as we have seen, 

 acquired variations are caused by external in- 

 fluences directly affecting it. Now, the heredi- 

 tary material is also life substance, and it is 

 plainly a possibility for us to imagine that this 

 germ material is also subject to influences from 

 the conditions surrounding it. That such varia- 

 tions do occur appears to be hardly doubtful, 



