46 ANNALS NEW YORK ACADEMY OF SCIENCES 



rise of the freezing point equal to that produced in the dog-fishes after 

 immersion in fresh water. It does not seem that in immersion sufficient 

 water has been added to the blood to cause the above lowering of the 

 freezing point. It may, however, be objected that the calculation of the 

 percentage of water in the two cases does not present the matter in its 

 true light. Any addition of water to the blood will separate the cells in 

 the blood to the same degree that it dilutes the soluble substances in the 

 blood. The determination of the dry weight of the blood, therefore, would 

 give a more nearly correct idea of the degree to which the solid substances 

 of the blood are diluted. Normal blood contains 135.2 parts of dried 

 material p. m., while the blood from fishes immersed in fresh water con- 

 tains 115.2 parts of dried material p. m. That is, the blood after immer- 

 sion of the animal in fresh water contains 14.8 per cent less dried ma- 

 terial than the normal blood. This means first of all less corpuscles ; but 

 it also means 14.8 per cent less organic and inorganic substances. It is 

 the inorganic substances in solution which determine in great part the 

 osmotic pressure of the blood. From this standpoint, then, the dilution 

 of the blood has caused a reduction of 14.8 per cent in the osmotic pres- 

 sure of the blood; but such a dilution is insufficient to account for the 

 rise of the freezing point of the blood actually observed, i. e., 21.9 per 

 cent. It must be concluded, then, that this is not altogether due to mere 

 dilution of the blood by the absorption of water. 



CHANGES IN THE NITROGEN" CONTENT OF THE BLOOD 



A comparison between the organic solids of normal blood and those of 

 the blood after the immersion of the fish in fresh water would also be an 

 index of the dilution of the blood ; but the amount of nitrogen present is 

 indicative of the amount of organic material, and therefore I concluded 

 to make determinations of the nitrogen. I wish to thank Dr. W. Denis 

 of the Laboratory of Biological Chemistry of the Harvard Medical School 

 for suggestions as to a modification of the Folin micro-chemical method 

 for the determination of urea which I used in making the nitrogen deter- 

 minations. After a sample of normal blood was taken, the fish was placed 

 in fresh water until near death. A second sample was then drawn from 

 the caudal artery. Table XVII shows the results of the analysis. 



