PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 483 



indifferent substances (sugars, e. g.), are applied to Stentor, permits us 

 to make at least the following inference. Shrivelling is due to loss of 

 water from the cell to the solution outside it, and this movement of water 

 proves that the Stentor under these osmotic conditions is permeable to 

 ivater, a fact which it might perhaps have been permissible to assume 

 rather than demonstrate. But whether loss of those salts which have 

 unbalanced partial pressures was also a factor in the process of destruc- 

 tion by concentrated solutions, is a more difficult question to decide from 

 the evidence. The conditions here are so closely related to those in the 

 milk-sugar experiments that I will consider them in connection with the 

 latter. 



We have now considered the conditions that prevail at opposite ends of 

 the concentration curve, and shall next proceed from both regions towards 

 the isotonic or normal region. That portion of the curve which extends 

 from distilled water up to those osmotic pressures which are approx- 

 imately isotonic with the natural culture media from which the animals 

 for experiment originate, I shall term the hypisotonic range. The condi- 

 tions here require separate description, which I will therefore defer till I 

 have given (in the next section) the experiments on the lower concentra- 

 tions of single and combined salts. 



There will remain, then, the question of the effect and the mode of 

 action of those concentrations which lie in the hyperisotonic range (above 

 about 200 molecular parts of calcic chloride in 100,000) of the curve. 

 A comparison of the mean results presented on the one hand by the 

 curves (p. 400) for the four salts, and on the other hand by the milk-sugar 

 experiments, shows that we have to distinguish between two well-marked 

 classes of effects. The application of milk sugar in hyper isotonic concen- 

 tration was practically harmless, whereas like concentrations of the four 

 salts were destructive. Mean results of unity, or something above unity 

 in the former case, and of zero in the latter, show the strong contrast be- 

 tween the two kinds of bodies. The curves (p. 473), taken in connection 

 with the sodic chloride control, give sufficient indication of the general 

 reaction of Stentor to these concentrations to show what would have 

 been the effects obtained from a simultaneous trial of each of the font- 

 salts in parallel with each test with milk sugar. Mean results of zero 

 would have been their uniform outcome. 



In what way shall we picture to ourselves the processes that bring 

 about these contrasted effects? If Stentors be removed from their 

 native mass-culture liquid to a solution of a single salt of higher concen- 

 tration, what processes follow ? 



