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. 



