PuHysioLoGicaL Errictency or IsosMOoTIC 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 isosmotie with the sea-water in Pacific 
Grove. Yet a 0.94 m saccharose solution was not physiologi- 
eally 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. 24 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 
: Percentage of 
Constitution of the Solution Eggs That 
|Produced Larvae 
50 c.c.4m LiCl +6 c.c. Qim LiCl...-....-.-+------ 5 
50 c.c.4m LiCl +7 c.c. Pesg tii] Oil Gilly cee eR eM On Ia oA 7 
50 c.c.4mKCl +7 ¢.c. Sir WO lei ae oils a 1 
50 c.c.mKCl +8 c.c. 22m CGI os Pais eens 60 
50 c.c. } m MgCl. +6 c.c. Fim MgCh.....-----+--->- | 50 
50 c.c. } m MgCl.+7 c¢.c. 2i-m MgCh.:...---5:s-++-= 80 
50 c.c. } m CaCl. +6 ¢.c. 25 
50 c.c. } m CaCl +7 c.c. 94m CaCl. ..-:--- 22s eres: 90 
