178 THE FITNESS OF THE ENVIRONMENT 



ingly osmotic pressure is commonly estimated 

 with the help of this relationship. In the 

 following table the facts regarding blood sera 

 of certain animals are collected. 1 



Depression of the Freezing Point of Blood Serum 



Degree 



Man 0.526 



Cow 0.585 



Horse 0.564 



Pig 0.615 



Rabbit 0.592 



Dog 0.571 



Cat 0.638 



Sheep 0.619 



In man the freezing point depression of the 

 blood is, under ordinary circumstances, practi- 

 cally constant, and there can be no doubt that 

 such is the case for all highest organisms. 

 Accordingly the differences in the above table 

 may be taken to indicate slight constant dif- 

 ferences between the different species. 



The marine animals, except a few of the 

 vertebrates, are adjusted in their osmotic 

 pressures to the water which surrounds them. 

 As in the following table so in another lo- 

 cality where the freezing point of the water 

 was —1.9° the body fluids of the animal 

 were again found to agree with it. It is 

 therefore evident that constancy of osmotic 

 1 Hober, "Physikalische Chemie der Zelle und der Gewebe." 



