22 HEREDITY. 



very clear, that in this way cells and cell-complexes may special- 

 ize. From the very beginning of development, cells on the 

 outside of the embryo must in this respect be very differently 

 situated from cells, which are not in direct contact with the 

 surface. Cells at one pole of the embryo, may be under very 

 different conditions in respect to available food-supply. Even 

 differences of short duration may lead to lasting differentiation, 

 if the quantitative relation between genes in the different cells 

 induced by the difference, makes the cells react in a different 

 way to similar opportunities. 



The phenomena of immunization find a ready explanation 

 on the theory, that the genes are autokatalisators. Just as we 

 can imagine how a cell can convert some materials with the aid 

 of a gene A into this substance A which may be a sugar, and 

 therefore, becomes able to convert still more of these same 

 materials into this sugar, so can we imagine how a toxic sub- 

 stance introduced in small quantities, can be used by some cells 

 in the upbuilding of one or more of the substances, which in 

 these cells are genes. A small quantity of a toxic substance, too 

 small to harm the life of the individual, is so converted into 

 the harmless substance of gene P, and after this transformation, 

 the individual is able to assimilate far greater quantities of the 

 toxic substance into P, with the aid of the quantity of P present, 

 before it has any harmful effect. It is possible, that what is 

 called the anti-toxin is an excess of a certain gene, which is 

 composed of "ingredients" taken mostly from the toxic sub- 

 stance introduced. 



It is unsafe to let our fancy roam too far in these purely 

 speculative fields. But after this brief tentative explanation of 

 functional excitation and differentiation, we would like to 

 point out, how under the assumption that genes are relatively 

 simple chemical substances, protoplasm being an emulsion of 

 these substances, the difference of behaviour under selection 

 between uni-cellular and multi-cellular organisms, admits of an 

 explanation. In the first place, it is conceivable how a uni-cellu- 

 lar organism, a bacterium, gradually adapts itself to a new 



