DISCOVERY OF THE PROTOZOA 109 



contributions of these and other observers we enter the 

 modern epoch. 



The importance of these animals in affording a field for 

 experimentation on the simplest expressions of life has al- 

 ready been indicated. Many interesting problems have 

 arisen in connection with recent studies of them and, as a 

 consequence, a separate division of biological study desig- 

 nated protozoology is recognized. The group embraces the 

 very simplest manifestations of animal life, and the experi- 

 ments upon the different forms light the way for studies 

 of the vital activities of the higher animals. Some of the 

 protozoa are disease producing; as the microbe of malaria, 

 of the sleeping sickness, etc., while, as is well known, most 

 diseases that have been traced to specific germs are caused 

 by plants the bacteria. Many experiments of Maupas, 

 Calkins and others have a bearing upon the discussions 

 regarding the immortality of the protozoa, an idea which 

 was at one time a feature of Weissmann's theory of heredity. 

 Binet and others have discussed the evidences of psychic 

 life in these micro-organisms, and the daily activity of a 

 protozoan became the field for observation and record in 

 an American laboratory of psychology. The extensive stud- 

 ies of Jennings on the nature of their responses to stim- 

 ulations form a basis for some of the discussions on animal 

 behavior. 



