44 



ANNALS NEW YORK ACADEMY OF SCIENCES 



CHANGES IX THE SPECIFIC GRAVITY OF THE BLOOD 



The method of Hammerschlag was used in the determination of the 

 specific gravity of the blood of Mustelus nnder normal and experimental 

 conditions. After the normal specific gravity of the blood of each speci- 

 men was obtained, the fish was placed in fresh water nntil near death. 

 Each value of specific gravity given below is the average of four or five 

 determinations. 



Table XV. — Shoiving the specific gravity of the hlood of Mustelus in sea-nater 

 and after immersion in fresh water 



A — Normal specific 

 gravity of blood 



B— Specific gravity of blood 

 in fresh water 



No. 1 = 1.0499 

 No. 2 = 1.0448 

 No. 3 = 1.0452 



1.0483 

 1.0359 

 1.0410 



Average = 1.0466 



1.0417 



A fall in the specific gravity of the blood is shown to have taken place 

 after immersion of the fish in fresh water. The blood is therefore more 

 dilute. 



CHANGES IN THE PERCENTAGE COMPOSITION OF THE WATER AND THE 



SOLIDS OF THE BLOOD 



It has been shown that profound changes in the molecular concentra- 

 tion of the blood take place when Mustelus is immersed in fresh water 

 and concentrated solutions of sea-water. To what are these changes due ? 

 Fredericq (^04) concluded that they were caused by absorption of water 

 into the blood. Centrifuge measurements of the blood of Scyllium modi- 

 fied by immersion of the animal in diluted sea-water, appeared to show an 

 increase in the relative quantity of plasma. Dakin ('08) held the same 

 view, for he claimed that the modifications in the osmotic pressure of the 

 blood which took place when Acanthias had been immersed in fresh water 

 were due to the blood gaining water, and that equilibrium between the 

 internal and the external medium was established by the gain or loss in 

 water being counterbalanced by absorption followed by secretion from 

 the kidneys. 



If the modifications in the osmotic pressure of the blood be due merely 

 to the addition or subtraction of water from the gills, then the gills are 



