26O WALTER E. CARREY. 



The osmotic pressure of the blood and body fluids of inverte- 

 brates is due exclusively to the salts which are in solution, the 

 proteid molecules being so large that they exert no appreciable 

 osmotic pressure. Analyses made by L. Fredericq 7 show that 

 the salts in the blood of a large number of invertebrates are pres- 

 ent in the same concentration as in the sea water. Although the 

 blood of selachians has a freezing point approximately the same as 

 that of the sea water, the salts are present in much smaller amount, 

 1.6 per cent, to 2.3 per cent, according to different analyses. 

 The high osmotic pressure is maintained by the presence of a 

 large and variable amount of urea (23 per cent., V. Schroeder, 24 

 Quinton, 20 Rodier, 22 Fredericq 9 ). 



Tcleosts.- -The blood of all teleosts examined showed a low 

 osmotic pressure which, in round numbers, approximated one 

 half that of the sea water.* In Table III. are given the extreme 

 variations in the freezing point for individuals of each species. 



TABLE III. 



The results of all these investigations on marine animals agree 

 with those of F. Bottazzi 1 and of Fredericq 9 at Naples. These 

 investigators found that invertebrate blood froze at 2.03 as 

 did also that of selachians, while teleost blood showed J = 

 1.04. The slightly greater depression of the freezing point 

 found by these authors is to be accounted for by a greater con- 

 centration of the sea water at Naples than at Woods Hole. 



VARIATIONS IN OSMOTIC PRESSURE OF THE BLOOD DUE TO 



CHANGES IN THE CONCENTRATION ON THE 



EXTERNAL MEDIUM. 



The analyses of L. Fredericq 7 showed that the concentration of 

 the salts in the blood of invertebrates varied with the concentration 



* Incidentally it was observed that the red corpuscles of teleosts were crenated by 

 5ea water. 



