THE LIVING MACHINE BUILDING FACTORS. 161 



not so easy to see how this germ plasm can un- 

 dergo variation. The conditions which surround 

 the individual would affect its body, but it is not 

 easy to believe that they would affect the ger- 

 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 fu- 

 ture use in reproduction. How could any changes 

 in the environment of the individual have any ef- 

 fect upon this dormant material stored within it ? 

 But if we are correct in regarding this germ mate- 

 rial in the reproductive bodies as the basis of 

 heredity and the guiding force in development, 

 then it follows that the only way in which con- 

 genital 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 char- 

 acters ; and if there are any congenital variations 

 from its parents, they must be due to some varia- 

 tions in the germ plasm. In other words, in order 

 to explain congenital 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, ac- 

 quired variations are caused by external influ- 

 ences directly affecting it. Now, the hereditary 

 material is also life substance, and it is plainly a 

 possibility for us to imagine that this germ mate- 

 rial is also subject to influences from the condi- 

 tions surrounding it. That such variations do 



