172 The Mechanistic Conception of Life 



which are needed for the preservation of animal life, play the 

 role of nutritive salts. Experiments which I made on a small 

 marine fish, Fundulus, proved beyond question that this is not 

 the case. If the young, newly hatched fish are put into a pure 

 solution of sodium chloride of the concentration in which this 

 salt is contained in sea-water, the animals very soon die. If, 

 however, KCl and CaCl, be added to the solution in the right 

 proportion, the animals can live indefinitely. These fish, 

 therefore, behave in this respect like Gammarus and the tissues 

 of the higher animals, but they differ from Gammarus and the 

 majority of marine animals inasmuch as the fish can live long, 

 and in some cases, indefinitely, in distilled and fresh water, 

 and certainly in a very dilute solution of sodium chloride. 

 From this fact I drew the conclusion that KCl and CaCU do not 

 act as nutritive substances for these animals, that they only 

 serve to render NaCl harmless if the concentration of the latter 

 salt is too high. I succeeded in showing that as long as the 

 sodium chloride solution is very dilute and does not exceed the 

 concentration of m/8, the addition of KCl and CaClg is not 

 required. Only when the solution of NaCl has a concentration 

 above m/8 does it become harmful and require the addition of 

 KCl and CaCl,. 



The experiments on Fw?2c?w7ws, therefore, prove that a mixture 

 of NaCl + KCl H-CaClo does not act as a nutritive solution, but 

 as a protective solution. KCl and CaCla are only necessary in 

 order to prevent the harmful effects which NaCl produces if 

 it is alone in solution and if its concentration is too high. We 

 are dealing, in other words, with a case of antagonistic salt 

 action; an antagonism between NaCl on the one hand and KCl 

 and CaCl^ on the other. The discovery of antagonistic salt 

 action was made by Ringer, who found that there is a certain 

 antagonism between K and Ca in their action on the heart. 

 When he put the heart of a frog into a mixture of NaCl + KCl 

 he found that the contractions of the heart were not normal, 



