4 8 



C. M. CHILD. 



posterior as well as the anterior vacuole region swells. Increase 

 in alkalinity accomplishes the same result as increase in con- 

 centration of KCN, i. e., it increases susceptibility. In other 

 words, when the concentration is so low that the animals die 

 very slowly only the anterior vacuole region undergoes swelling 

 before the death and disintegration of the rest of the body. 



In still higher concentrations, e. g., KCN 0.04 m. the animals 

 die very soon, hyaline droplets appear on all parts of the body 



23 



and in a few seconds nothing remains but the entoplasmic granules 

 and the meganucleus more or less surrounded by the semi-fluid 

 hyaline substance in rounded masses or droplets, apparently 

 with a surface membrane. Sooner or later the droplets burst, 

 apparently in consequence of rupture of the membrane, and the 

 substance of the body spreads through the water. In such cases 

 a gradient does not usually appear because the concentration is 

 sufficiently high to kill all parts at the same time or nearly so. 



DISCUSSION. 



It is evident from the preceding sections that a more or less 

 definite axial gradient in susceptibility to KCN exists in all of the 

 forms examined. These forms represent the four orders of 

 ciliate infusoria, Heterotricha (Stentor), Hypotricha (Stylonychia, 

 Euplotes, etc.), Peritricha (Vorticella and Carchesium) and Holo- 

 tricha (Paramcscium) , so that the existence of an axial gradient 

 is evidently characteristic of the group. 



