116 



PROTOZOOLOGY 



Reaction to chemical stimuli. When methylgreen, methylene 

 blue, or sodium chloride is brought in contact with an advancing 

 amoeba, the latter organism reacts negatively (Jennings). Jen- 

 nings further observed various reactions of Paramecium against 

 chemical stimulation. This ciliate shows positive reaction to weak 

 solutions of many acids and negative reactions above certain con- 

 centrations. For example, Paramecium enters and stays wdthin the 





>M:^^M«. 



Fig. 49. Reactions of Paramecium (Jennings), a, collecting in a drop 

 of 0.02% acetic acid; b, ring-formation around a drop of a stronger solu- 

 tion of the acid; c, avoiding reaction. 



area of a drop of 0.02 per cent acetic acid introduced to the prepara- 

 tion (Fig. 49, a) ; and if stronger acid is used, the organisms collect 

 about its periphery where the acid is diluted by the surrounding 

 water (Fig. 49, h). The reaction to chemical stimuli is probably of 

 the greatest importance for the existence of Protozoa, since it leads 

 them to proper food substances, the ingestion of which is the found- 

 ation of metabolic activities. In the case of parasitic Protozoa, 

 possibly the reaction to chemical stimuli results in their finding 

 specifi.c host animals and their distribution in different organs and 

 tissues within the host body. Recent investigations tend to indicate 

 that chemotaxis plays an important role in the sexual reproduction 

 in Protozoa. 



