480 PROCEEDINGS OF THE AMERICAN ACADEMY. 



One further feature of these observations I desire to emphasize here. 

 The increase in value of L above observed did not continue indefinitely, 

 but was only initial, at least in the above intensity. To the meaning of 

 this fact I shall recur (p. 505). 



Sufficient data have now been secured at different points on the con- 

 centration curve to furnish at least' the basis for a general interpretation, 

 and I therefore defer the description of further experiments upon com- 

 bined salts until after the following general discussion. 



VI. Discussion of Single Salts and Water. 



I desire to interpret the preceding experiments from two initially 

 different points of view. From one standpoint I shall attempt a physico- 

 chemical explanation as far as the facts warrant ; from the other I shall 

 seek to explain the same and additional facts as the expression of specific 

 adjustments in the metabolism of S ten tor. The two views are certainly 

 complementary to each other. Whether or not they can be merged into 

 one, I prefer to leave to the reader's opinion upon a fundamental question 

 in biology. 



The results of the two experiments last described, together with others 

 that are similar, show that when Stentors are transferred from their 

 ordinary mass-culture medium to very pure distilled water, an increase 

 in the conductivity of the water takes place during at least the initial 

 hour or two. What is the source of this variation ? The control shows 

 that it cannot be from any part of the test-cell. It might be urged that 

 the observed increased conductivity was due to the unavoidable intro- 

 duction of a small amount of the culture medium with the Stentors, 

 notwithstanding the multiple transference of the animals ; for the con- 

 centration in the immediate vicinity of a solid object, whether animate or 

 inanimate, would be much greater than in the surrounding medium, 

 generally, and furthermore the ciliate covering of Stentor would certainly 

 increase considerably the danger of the retention by the animal of more 

 highly concentrated solution immediately around it at each transfer. 

 But that this cannot be the true explanation of increased conductivity 

 is evident from the fact that this increased conductivity does not manifest 

 itself promptly, but only after the lapse of some time. These facts leave 

 us room for no other explanation as to the cause of increased conductivity 

 than the metabolism of the organisms themselves. Reflection upon the 

 change in the conditions presented by the Stentors when transferred 

 shows, furthermore, that this conclusion is entirely reasonable. 



There is abundant evidence that the culture media contain salts. The 



