METHOD OF OPERATION 137 



There are indeed such special conditions working against 

 the inheritance of environmental effects in multicellular 

 organisms. As compared with unicellular organisms, the 

 dijfiferences that are significant in this respect are mainly the 

 following. The unicellular organisms are minute, their genie 

 materials are in close relation with environmental agents. The 

 higher organisms are relatively enormous. Only the genie 

 materials of their germ cells can affect the characteristics of 

 descendants, and the germ cells are hidden deeply within the 

 body, protected from the action of most outer agents. Be- 

 tween parent and offspring a long series of cell generations 

 intervenes, during which there is opportunity for loss of any 

 modifications induced in the germ cells of the parent. These 

 conditions operate against the inheritance of the effects of 

 environmental agents in higher organisms. 



Weighing more strongly than any of these considerations 

 perhaps is the fact of the great weight of negative evidence 

 from observations and experiments directed toward testing 

 the inheritance of environmental acquirements. No subject 

 in biology has been worked on more than this. The over- 

 whelming majority of the results are negative. Sometimes the 

 discovery of the inheritance of acquired characters is an- 

 nounced; usually it is discovered later that an error under- 

 lies the interpretation. As yet outstanding are the results of 

 William McDougalP on the inheritance of the effects of 

 training on the rat. These if accepted at face value would 

 demonstrate the inheritance of acquired characters. In view 

 of the history of many such investigations in the past, one can 

 hardly do otherwise than expect that some error of interpre- 

 tation will be found to underlie these results; and that they 

 will be found not to demonstrate the inheritance of the effects 

 of training. It may turn out that the inheritance of environ- 

 mental adaptations is limited to unicellular organisms. 



