OSMOTIC PRESSURE OF SEA WATER. 26 1 



of the salt water from which the animals were taken. This was 

 most strikingly shown by the blood of Carcimis nuznus taken 

 from brackish water and from sea water. In the course of our 

 investigations it was found that differences in the freezing point 

 of the blood of invertebrates accompanied differences in the freez- 

 ing point of the sea water from which they were taken ; thus the 

 blood of lobsters taken from the "basin" traps showed J = 



1.82, but when taken from the "eel pond" J = 1.77. A 

 decrease in the concentration of the water from the laboratory 

 tap, due to severe rains, caused exactly the same changes in the 

 freezing point of lobster's blood, J became - 1.78. An increase 

 in the osmotic pressure of the blood of Liiiiulus was induced by 

 a two days' exposure to the drying influence of the atmosphere. 

 The freezing point went down to 1.90. The blood of a 

 Liimtlus kept alive for two weeks in a damp cellar froze at 



2.03, the normal J = 1.82. Both diurnal and seasonal 

 changes occur in the concentration of the water of San Francisco 



o 



Bay, Cal. (taken near the Golden Gate), and the perivisceral fluid 

 of starfish shows exactly the same changes ; thus on March 17, 

 1904, J = 1.47 at high tide but at low tide only - 1.385. 

 On September 23, J = - - 1.80. 



With these facts as a starting point it was decided to test the 

 freezing point of the blood when the animal was subjected to a 

 large decrease or increase in the osmotic pressure of the external 

 medium. 



Dilution of the sea water was first tried and after a longer or a 

 shorter immersion the animal was removed and the freezing point 

 of the blood was determined. The changes which are thus 

 induced are given in Table IV. 



In nearly every experiment the animals were kept in the dilute 

 medium until collapse set in, but in a majority of cases they were 

 able to revive when replaced in normal sea water. Liinulus and 

 Sycotypns are particularly hardy and it is noted that the freezing 

 point of their blood changes very quickly until in some cases it 

 is approximately equal to that of the external medium. When 

 the external medium is very dilute death may occur before this 

 equalization takes place ; this was particularly true in the case 

 of Hojnanis, which is very susceptible to a change in the con- 



