70 



PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



meant by Ehrenberg, the protozoa today offer a field of research in 

 physiology that is quite unique, for while they epitomize the vital 

 activities of the higher animals, these activities are of such simple 

 types that they may be more easily observed and correlated with the 

 ordinary reactions in physics and chemistry, reactions which we do 

 not associate with the vital processes of the higher animals. 



The warning may not be out of place here that despite the simplicity 

 of function in the protozoon, and the analogy with reactions in the 

 inorganic world, there is, nevertheless, a power of acting as a whole, 

 a power of coordination combined with factors of adaptation and 



Fig. 21 



Food-taking. A, after Pfenard; B and C, after Biitschli. A, Raphidiophrys elegans, H. and L.; 

 B, Oikomonas termo, Ehr.; C, Didinum nasutum, O. F. M.; f, food particles. 



evolution, which permit of development into more and more com- 

 plicated structural units, which arises, per se, in all protoplasm, and 

 raises it immeasurably above the most complex of non-living sub- 

 stances; this power of adaptation is an inherent characteristic of 

 living matter, transcending physical or chemical analysis, and justify- 

 ing, perhaps, the often abused term vitalism. It must not be forgotten 

 that, notwithstanding the simplicity of the single functions, the proto- 

 zoa are units exhibiting a complex of these activities and an harmonious 

 working of them all, no less surely than fish, bird, or mammal. In 

 studying these simple functions it is well not to forget that each belongs 

 in the same category of activities as the functions of much more highly 



