90 Life and Death, Heredity and Evolution 



color was produced that was permanent. When the bac- 

 teria were restored to their natural conditions they re- 

 mained white, no matter how long the culture was continued. 

 And with certain other chemicals the bacterial color became 

 permanently a darker red; although restored to normal 

 conditions and kept there for hundreds of generations, the 

 acquired dark color persisted. 



This work proves therefore that in bacteria by the action 

 of the environment definite changes that are hereditary can 

 be produced. From a single race, by subjecting parts of it 

 to these diverse agents, a number of hereditarily diverse 

 races are obtained. 



In this case the alteration is evidently a change in the 

 chemical processes of the organisms. The red color of this 

 bacterium is not in the body of the creature, but is due to 

 some substance produced by it, which colors the material on 

 which the organisms live. In the experiments the effective 

 substances changed the chemical processes so that the 

 bacteria no longer produced this substance, or produced 

 one of another color. 



Similar in the fact that they deal with peculiarities that 

 are visible to the eye are certain experiments of Toenniessen 

 (1915). He investigated a certain strain of the bacillus 

 which produces pneumonia. This organism produces a quan- 

 tity of mucus, which forms a thick envelope in which the 

 cell is imbedded; the volume of this envelope is perhaps 

 several hundred times that of the cell itself. When the 

 organisms are cultivated for a long time in dense colonies on 

 agar, the products of their nutritive processes collect, until 

 they decrease the organisms' power to produce the envelope 

 of mucus. After a time some of the bacteria are found with 

 only a thin envelope, others with none at all. 



If these modified bacteria are transferred to normal con- 



