550 STUDIES IN GENERAL PHYSIOLOGY 



pressure of a NaNO 3 and KNO 3 solution which is just able 

 to prevent growth in Spyrogyra is lower than that of a sugar 

 solution which renders growth impossible. Hence he con- 

 cludes that NaNO 3 is not harmless for Spyrogyra. 1 In this 

 case, of course, the concentration of Na ions was much 

 greater than in the blood or in sea-water. It is, however, 

 easy to give striking illustrations of the fact that a pure 

 NaCl solution is a strong poison. In a former paper I have 

 shown that Fundulus, a marine fish, can endure an astonish- 

 ing 1 increase in the concentration of sea- water. An addition 



O 



of 5 per cent. NaCl to sea-water does not injure the animal. 2 

 I selected it for testing my conceptions concerning the metal 

 proteids. I found that it dies in a short time in a pure NaCl 

 solution of the same concentration as that in which this salt 

 exists in the sea- water. 3 In ^n solutions of NaCl which 

 were diluted with various quantities of distilled water, the 

 animals lived the longer the greater the dilution was, and in 

 distilled water the young fish lived indefinitely. The 

 following table shows the duration of life of these fish in 

 pure NaCl solutions of various concentrations: 



TABLE I 



AVERAGE DURATION OF LIFE OF YOUNG FUNDCLUS IN PURE NaCl SOLUTIONS OF 



DIFFERENT CONCENTRATION 



i TRUE, Botanical Gazette, 1898, p. 407. 



2LOEB, Archiv fur die gesammte Physiologic, Vol. LV (1894), p. 530. 



3 For these experiments the young fish which had just hatched were used. As 

 they were less than a centimeter long, their mass was small compared with the 

 volume of the solul ion. 



