512 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The extrusions with sodic sulphate are peculiarly dense (heavy), deep 

 in color, and of strong consistency. That with chloroform has much the 

 same character, and well illustrates the formation of an envelope of this 

 matter around the cell. Most of the salts and the acids give lighter- 

 colored and less consistent extrusions. 



The addition of calcic chloride to sodic sulphate solutions raises the 

 concentration of the latter required to produce extrusion, and in sufficient 

 quantity prevents this effect of sodic sulphate altogether. 



This result demonstrates clearly enough that this is not an osmotic 

 phenomenon, like the laking of blood corpuscles with some salts. Even 

 in the latter case certain reagents, for example ammonic chloride (Ham- 

 burger, : 02, p. 169), cause extrusion in any concentration. For Stentor 

 the substances tested form a series, at one end of which practically any 

 concentration results in extrusion, at the other no concentration is able 

 to produce this result. The series expresses the animal's adjustment to 

 the different substances in regard to this phenomenon. The extruded 

 substance is of such nature that simple osmotic change does not cause its 

 rejection from the cell. The conditions point to a chemical process. It 

 is well known that different classes of proteids exhibit characteristic solu- 

 bilities or insolubilities toward different salt solutions. By means of 

 these they are separable from one another. In view of these facts the 

 suggestion is ventured that the extruded coloring matter is a proteid 

 separated from the living protoplasm by some salts, and not at all by 

 others. 



XL General Summary. 



1. In the growth and normal action of free-living cells, the salt con- 

 tent of the liquid medium in which they live is a most important factor. 



2. In cultures of Infusoria the different stages in the development 

 of a culture have each their characteristic animals. The fermentation 

 of food material in the early stages of a culture prevents the growth of 



