PHYSIOLOGICAL EFFICIENCY OF ISOSMOTIC SOLUTIONS 131 



tions which were 1.135 N, e.g., a mixture of 40 c.c. of such 

 a cane-sugar solution +10 c.c. of sea-water. He insisted that 

 these solutions were isotonic for the sea-urchin eggs, since 

 their molecular concentration was equal to that calculated 

 from the depression of the freezing-point of the sea-water which 

 he used. Our experiments show that a saccharose solution 

 which is theoretically isosmotic with the sea-water is neverthe- 

 less physiologically hypertonic. Theoretically a 0.94 m sac- 

 charose solution is isosmotic with the sea-water in Pacific 

 Grove. Yet a 0.94 m saccharose solution was not physiologi- 

 cally isotonic with sea-water, but acted physiologically like a 

 solution equal in osmotic pressure to a mixture of 50 c.c. sea- 

 water +8 c.c. 2| m NaCl, i.e., a hypertonic solution. This dis- 

 crepancy can be explained partly or wholly from the fact that 

 the osmotic pressure of cane-sugar solutions is greater than we 

 should expect from their molecular concentration (according 

 to the direct measurements of Lord Berkeley and of Morse). 

 This discrepancy between the theoretical and real osmotic pres- 

 sure of cane-sugar solutions may possibly increase with the 

 concentration. 



In order to elucidate whether besides the merely physical 

 a physiological factor was also involved in this discrepancy 

 between theoretically isosmotic and physiologically isotonic 

 solutions some experiments with other substances were tried. 



TABLE XVI 



Constitution of the Solution 



50 c.c. \ m LiCl +6 c.c. 2^ m LiCl . . 

 50 c.c. \ m LiCl +7 c.c. 2| m LiCl . . 

 50 c.c. | m KC1 +7 c.c. 2 m KC1 . . 

 50 c.c. \ m KC1 +8 c.c. 2^ m KC1 . . 

 50 c.c. \ m MgCl 2 +6 c.c. 2| m MgCl, 

 50 c.c. | m MgCl 2 +7 c.c. 1\ m MgCl 2 . 

 50 c.c. \ m CaCl 2 +6 c.c. 2| m CaCL. 

 50 c.c. \ m CaCl 2 +7 c.c. 2 m CaCl 2 . 



Percentage of 



Eggs That 

 Produced Larvae 



5 

 70 



1 



60 

 50 

 80 

 20 

 90 



