506 PROCEEDINGS OF THE AMERICAN ACADEMY. 



above experiment is inconclusive. It is not probable, however, that the 

 inward movement of water alone accounts for all the increase in conduc- 

 tivity. The probabilities are in favor of the permeability of the cell, for 

 it is not likely to possess a membrane j)ermeable to water alone. 



Upon the whole, the method by measuring conductivity is too general 

 to yield specific information upon permeability, because conductivity is 

 influenced by too many factors, and is affected by various salts. More- 

 over, as Hamburger (: 02, pp. 2.55, 259) has pointed out, under certain 

 conditions some exchange of ions between medium and cell could take 

 place without change in the conductivity of the former. 



An experiment similar to the above was attempted upon Paramaecia, 

 but these animals disintegrated under the process. Furthermore, two ex- 

 periments were made upon Spirostomum ambiguum. In the first experi- 

 ment the animals were placed in the same hypisotonic medium of di-sodic 

 phosphate -f potassic nitrate as that which was used for Stentor. The re- 

 sult showed a similar increase in conductivity. In the second experiment 

 the test-medium consisted of native culture liquid that had been filtered 

 through a washed filter and had then been well shaken for the purpose 

 of aeration. This was practically an isotonic medium, In a period of 

 1.7 hours no increase in conductivity was detected. This result lias two 

 important bearings. It indicates the correctness of the view above ex- 

 pressed that increased conductivity in the hypisotonic medium was due to 

 osmotic redistribution of salts and water. It furthermore indicates that 

 the respiratory activity of the animal, though constant, is not of such 

 quantitative or possibly qualitative nature as to increase the conductivity 

 of the medium within a short period of time. The motive for making 

 this experiment was to test the possibility that respiration by the cell as a 

 whole, or excretion by the contractile vacuole, might result in the accu- 

 mulation in the medium of measurable ionized products. The quantity of 

 these should increase continuously and uniformly, and its determination by 

 the measurement of conductivity would have been a valuable method for 

 the investigation of metabolism in Protozoa. Various determinations upon 

 isotonic media containing Stentors for longer periods than above described 

 were made, but the results were inconclusive. 



Expt., Dec. 13, 1902. 



The object of this experiment was to determine the permeability of 

 Stentor to chlorine. The method consisted in the estimation of the 

 change in the content of chlorine and in the degree of alkalinity of a 

 medium containing Stentors under isotonic conditions. This method is 



