SCOTT, STUDY OF CHANGES IN MUSTELIS CAN IS 



47 



Table XVII. — Nitrogen content of the hlood of dog-fishes in sea-water and 



after immersion in fresh water 



No. 



Length in 

 cm. 



Weight in 

 gm. 



A— Nitrogen in normal 

 blood. Mg. in 1 c. c. 



B — Nitrogen in blood after 



immersion in fresh water. 



Mg. in 1 c. c. 



1 



2 



3 



4 



72 

 74 

 69 

 74 



1077 

 1191 

 1049 

 1389 



22.697 

 22.775 

 23.150 

 23.812 



18.125 

 19.145 

 19.875 

 20.825 





Average 23.109 



19.493 



The average quantity of nitrogen in the normal blood of Mustelus is 

 23.109 mg. per c. c., while after the immersion of the fish in fresh water it 

 has fallen to 19.493 mg. This means that by immersion the blood has 

 lost 15.6 per cent of its nitrogenous matter. Haemoglobin is a large nitro- 

 genous component of the blood. It has already been shown that the blood 

 is not laked by the changes produced in its osmotic pressure by the fresh 

 water. The haemoglobin therefore cannot have left the blood. The 

 greater part of the remaining nitrogenous matter in the blood is present 

 in the proteins of the plasma. It is improbable that they diffuse out 

 through the gills. 



On the whole, the conclusion must be drawn that the dilution due to 

 the addition of water to the blood will account for a loss of but 15.6 per 

 cent in the substances in the blood, and also a rise in the freezing point 

 of but 15.6 per cent. 



CHANGES IN THE UEEA CONTENT OF THE BLOOD 



It has been known for some time that urea is present in unusually large 

 quantities in selachian blood. Thus von Schroeder ('90) found that the 

 blood of Scy Ilium contained 2.6 per cent urea, and this was afterward 

 confirmed by other investigators. Urea is usually regarded as a readily 

 diffusible substance. Its gram-molecular solution has about the same 

 osmotic pressure as sea-water, i. e., 22.4 atmospheres. When Mustelus is 

 immersed in fresh water, will the urea with its high osmotic pressure dif- 

 fuse through the extremely thin membranes of the gills and the capillary 

 blood vessels into the fresh water, with a A of but 0.025° ? Dr. Denis has 

 kindly made for me the following determinations of the urea in blood 

 which I obtained from four specimens of Mustelus under the above ex- 

 perimental conditions. Moreover, the blood was obtained from the same 

 fishes and under the same experimental conditions as described on page 

 — , where my determination of the total nitrogen in the blood is given. 



