THE REACTION OF ANIMAL CELLS TO CHEMICAL 



STIMULI. 



By Frank Hartman, Kansas City, Kan. 



\ S the field of zoology broadens, our increased knowledge of the 

 -^-^ structure and behavior of 'animal forms drives us deeper and 

 deeper into perplexing problems of life phenomena. The solution of 

 many of these problems is looked for in the study of the simpler 

 unicellular organisms. The fact that each one of these single- 

 celled creatures is a living unit and performs all of the processes 

 necessary to the maintenance of life makes them an attractive field 

 of investigation. 



It is the purpose of this paper to give a review of the work which 

 has been done on the Protozoa in their relation to chemical stimuli 

 and to give a few of the author's experiments on paramoecium. 

 Two different classes of experiments have been carried on — first, 

 the effect of temporary chemical stimulation on the individual 

 animal ; and second, the effect of both temporary and continued 

 chemical stimulation on the race. The second class of experiments 

 is manifestly more important. 



The effect of chemical stimulation on the individual has been 

 worked out by Jennings on various Protozoa. He has shown that 

 the theory of tropisms, including chemotropism, is false when ap- 

 plied to the ciliates. An attempt was made by earlier investigators 

 to make the reactions of the Protozoa conform to the tropism 

 scheme. Tropism, in this case, chemotropism, is a direct move- 

 ment or orientation of the animal towards, or away from, a diffusing 

 chemical. In this movement the lines of diffusion bear a direct 

 relation to the position and direction which an animal takes in 

 moving under the influence of a chemical. 



There is no doubt about the occurrence of chemotropism among 

 plants, but no animal whose behavior has been carefully studied 

 shows this simple reaction to chemicals. Jennings has demon- 

 strated this fact. Among the protozoans some chemicals stimulate 

 a motor reflex. This reflex action is a sudden backing, followed by 

 a rapid turning of the animal toward a particular side, the one op- 

 posite the mouth. When the concentration is great enough, most 

 chemicals start this motor reflex. In a majority of cases this ac- 

 tion removes the animal from the source of stimulus, because the 



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