492 PROCEEDINGS OF THE AMERICAN ACADEMY. 



of abscissas. Quite other conditions than the above, carrying with them 

 a different significance, are conceivable. The concentration at which a 

 substance begins to be favorable for the physiological processes of the 

 animal is shown by the point at which the upward curvature occurs. 

 Since these upward curvatures, and even the paths of the curves as a 

 whole, stand in the serial order above mentioned, Stentor must be best 

 adjusted to calcic chloride, next to potassic chloride, then to sodic chloride, 

 and least to magnesic chloride. It is not maintained that in another 

 series of experiments the curvature would occur at the same absolute 

 points of concentration, or that the mean results would reach unity at the 

 same points ; but it is maintained that, if comparative experiments with 

 corresponding concentrations of two or more of the four salts be made 

 upon Stentors having the same physiological condition, although the 

 results obtained might be numerically different, they would continue to 

 stand in the same relative order, the results most favorable to the animal 

 being those for calcic chloride. In other words the curves are valid, as 

 I have previously explained, only relatively, not absolutely. Further 

 evidence that calcic chloride favors the life processes of Stentors more 

 than the other salts do can be found in the next following section. 



In the case of milk sugar we have a different form of adjustment. 

 The physiological salts being natural constituents of the organisms, adjust- 

 ment to them may be distinguished from that to milk sugar, which is 

 probably an artificial, though certainly an indifferent, substance for 

 Stentor. 



The significance of adjustments for the internal organization of the 

 cell will be discussed in the following section. 



VII. Observations on Single and Combined Salts. 



The experiments of the present section were made with a twofold aim. 

 First, it was desired to complete the physico-chemical description of the 

 action of salts in the hypisotonic range of concentration, the aim being 

 here theoretical ; secondly, to determine the normal adjustments of Stentor 

 to physiological salts. The purpose was to find such salts and such com- 

 bined proportions of these as seemed most favorable to the life-processes 

 of the animal. From this would result the determination of, first, the 

 qualitative range of adjustment, that is, the number and kinds of sub- 

 stances to which the animal reacts normally ; secondly, the quantitative 

 range of concentration that was normal for the animal in the case of each 

 salt. The two series of facts constitute the ground for the theory of 



