HEREDITY. 23 



substance in its culture-medium, through the fact that it can 

 originally make use of very small quantity s of it, transforming 

 it or part of it into N under the influence of minute quantities 

 of N present in its protoplasm as a gene. 



We can imagine how, with the relative increase of N, and 

 repeated cell-divisions, the capacity of the strain of bacteria for 

 a splitting-up, or by an assimilation of the added substance, 

 finally is greatly enhanced. It is possible in this way, to explain 

 the process of adaptation of a clone of bacteria to a certain 

 sugar, a change from a form which leaves the sugar intact or 

 nearly so, to a strain capable of splitting it up. In the same way, 

 we can vaguely picture how a bacterium which originally did 

 not thrive as a parasite in an animal T. becomes in the course 

 of many cell-generations adapted to live in this same species T. 



A multi-cellular organism is less plastic. In the first place only 

 a fraction of the number of its cells are in direct contact with 

 assimilable substances ; in the second place, it is probable that 

 a complete set of genes is kept intact inside the nuclear mem- 

 brane. I should judge that organisms without nucleus should 

 be in a state of unstable genetic equilibrium. Autokatalytical 

 substances, entering the organism from without, not only can 

 increase in quantity within the. protoplasm and contribute to 

 the development in the same way as other genes, but in these 

 organisms they are not at a disadvantage as compared with 

 other genes. 



But even if we compare more highly organized uni-cellulars 

 with multi-cellular organisms, we see that there is a great differ- 

 ence in the course of heredity. Not only is the uni-cellular organ- 

 ism in intimate contact with its environment, but even those 

 cells of the multi- cellular which do come into contact with the 

 environment as a rule have no "future," that is to say, they 

 have no germ-cells in their descendants. This leads us to the 

 question of inheritance of effects of environment, and of spon- 

 taneous geno- variation, mutation. 



When we get rid of the notion that genes are necessarily 

 vital, complex things, which can vary, and can occur in latent 



