Role of Salts in Preservation of Life 171 



other, in both cases the duration of life is shortened by practi- 

 cally the same amount. 



If the crustaceans are brought into a pure solution of NaCl, 

 of the same osmotic pressure as the sea-water, they also die in 

 a,bout half an hour. If to this solution a little calcium chloride 

 be added in the proportion in which it is contained in the sea- 

 water the animals die as rapidly as without it. If, however, 

 both CaClj and KCl are added to the sodium chloride solution, 

 the animals can live for several days. The addition of KCl 

 alone to the NaCl prolongs their life but little. 



If KCl and CaClj are added to a cane-sugar solution isotonic 

 with sea-water, the animals die as quickly or more so than in the 

 pure cane-sugar solution. 



If other salts be substituted for the three salts the animals 

 die. The only substitution possible is that of SrClj for CaClj. 

 We find also that the proportion in which the three salts of 

 sodium, calcium, and potassium have to exist in the solution 

 cannot be altered to any extent. All this leads us to the con- 

 clusion, that in order to preserve the life of the crustacean 

 Gammarus, the solution must not only have a definite concentra- 

 tion or osmotic pressure but that this osmotic pressure must be 

 furnished by definite salts, namely, sodium chloride, calcium 

 chloride, and potassium chloride in the proportion in which 

 these three salts exist in the sea-water (and in the blood) ; this 

 fact could also be demonstrated for many other marine animals. 

 The relative tolerance of various cells and animals for abnormal 

 salt solutions is, however, not the same, a point which we shall 

 ■discuss later on. 



Ill 



What is the role of the salts in these cases ? The botanists 

 have always considered salt solutions as nutritive solutions. 

 It is a well-known fact that plants require definite salts, e.g., 

 nitrates and potassium salts, for their nutrition, and the ques- 

 tion now arises whether the three salts NaCl, KCl, and CaClj, 



