48 



ANNALS NEW YORK ACADEMY OF SCIENCES 



Table XVIII. — Urea content of the Wood of Mustclus cauls in sea-water and 



after immersion in fresh tcater for one hour (see Table X for 



sex, length, and weight) 





Urea in normal 



blood, 



grams p. m. 



Urea in blood after 



immer.«ion, 



grams p. m. in 



fresh water 



Fish No. 1 



15.4 

 15.8 

 15.0 

 15.6 



12.6 

 13.2 

 13.2 

 13.2 



a a 2 



" 3 



it (( ^ 





Average 



15.45 



13.05 





This means that the blood lost 15.5 per cent of its urea after immersion 

 in fresh water. The normal blood of Mnstehis contains 1.55 per cent of 

 urea. This has a freezing point of about — 0.45°, and 15.5 per cent of 

 this equals 7.3°. The change in the molecular concentration of the blood 

 is therefore due to other causes than a diminution in the urea. Moreover, 

 the diminution in the urea content is approximately the same as that of 

 the total nitrogen and solids, which, as has been said, indicates in all 

 probability the changes produced by dilution of the blood due to the ab- 

 sorption of water through the gills. These results also show that the 

 maximum change in the osmotic pressure of the blood is due to causes 

 other than its mere dilution. 



CHANGES IN THE SALT CONTENT OF THE BLOOD 



It has been concluded that sufficient water has not been absorbed to 

 account for the lowering of the osmotic pressure of the blood which my 

 experiments demonstrate to have taken place, when Mnstehis is im- 

 mersed in fresh water. Baglioni ('05 ) and others have shown that the 

 blood of the elasmobranchs that they studied contains about 2 per cent of 

 salts and 2.6 per cent of urea. Although both of these substances con- 

 tribute to the osmotic pressure of the blood and are readily diffusible, it 

 is generally held that neither diffuses into the external medium when the 

 fish is immersed in fresh water. Yet it has been shown in the preceding 

 experiment that a decrease of 15 per cent in the solids of the blood takes 

 place. Are the salts decreased to a like amount ? 



In a first series of experiments the blood was weighed, dried to constant 

 weight and ashed, and the ash was analyzed for chlorine by the Volhard 

 method. I wish to thank Dr. George F. White of Clark College and Mr. 

 W. J. Crozier of the College of the City of New York for valuable advice 



