No. 575] RESPONSES OF PLANTS AND ANIMALS 667 



enced Pasteur, who over eighty years later laid the 

 foundation for the modern epoch of development, by 

 combating a plague of diarrhoea in poultry (1880). 

 During the twenty years following*, various investigators 

 added noteworthy contributions, and about 1900 Ehrlich 

 and Morgenroth evolved the " side-chain theory" by 

 which a large number of possible conditions can be pre- 

 dicted and all the observed facts of immunity explained. 

 While not expressed in strictly chemical terms, the theory 

 and the experiments which support it are very important 

 both practically and theoretically. In recent years the 

 knowledge of immunity and comparable phenomena have 

 been greatly extended. Various workers (Pfeffer, Vol. 

 IT, p. 262) have shown similar phenomena in the increased 

 resistance of plants to poisons, thus making the responses 

 of plants and animals still more generally comparable. 

 Most recently workers on problems such as fertilization 

 (Lillie, 13), standing in close relation to the older germ- 

 plasm doctrine, have discovered facts belonging to this 

 field and made use of Ehrlich 's theory to explain the ob- 

 servations. This development has helped to confirm the 

 conclusion of some investigators that immunity phe- 

 nomena represent Important features of the chemical 

 mechanism of life. Adami has remarked, 



That a plague of diarrhoea in a poultry yard, studied hy a professor 

 of chemistry, should be the seed from which has grown the vast de- 

 velopment of later years is a strange fact, but a fact nevertheless. 



What was the attitude of pure science so called, of 

 germ-plasm doctrinairies, and biologists generally during 

 the long period which elapsed before they could make 

 use of his results? Clearly it was one of indifference, if 

 not disgust, toward the subject. The probable result of 

 such attitudes on the progress of the investigation of 

 immunity phenomena, had it not been for their immense 

 practical significance, is clear. They could not have 

 received their proper share of attention. Thus in the 

 pursuit of the analysis of the chemical mechanism of life 

 men who sought it directly have failed in this one impor- 



