SCOTT, STIDY OF f'//,l.A (;/;»V IN MUSTELl H (\{\/S (35 



blood. The chlorine of the blood has decreased nearly 26 per cent. This 

 probably means an excessive loss in salts, which would account for the 

 greater decrease in the osmotic pressure of the blood. 



We may next consider the contribution of the salts and urea to the 

 osmotic pressure of the blood. The usual impression one gets from a 

 perusal of the literature is that the osmotic pressure of the blood is due 

 almost wholly to the presence of crystalloids, i. e., chlorides and urea. 

 By the method of ashing, it is probable that some small part of the 

 chlorine is lost by volatilization. In the method used above for the de- 

 termination of the chlorine in serum, it is possible that a certain amount 

 of salts was retained by the diffusates. ^Nevertheless, every care was 

 taken to prevent error in the analyses. The determination of the urea 

 was likewise as carefully made. Dakin (^08) found that the blood of 

 Acanfhias vulgaris, the freezing point of which is almost identical with 

 that of Mustelus, contained 0.88 per cent chlorine. The serum of Mus- 

 telus blood contains, according to my analyses, 0.86 per cent chlorine. 

 Expressed in terms of sodium chloride, this means that there was present 

 1.424 per cent NaCl. The urea formed 1.55 per cent of the blood {i. e., 

 corpuscles and plasma). This is somewhat greater than the percentage 

 of salts. In the analyses given by other investigators, a greater amount 

 of urea than salts was also found. Moreover, when one takes into con- 

 sideration the differences in the osmotic pressure of the sea-water at the 

 stations where other investigations have been made, knowing selachian 

 blood to be approximately isotonic with its sea-water medium, one finds 

 that the change in the percentage composition of the salts and the urea 

 is proportional to the modification of the osmotic pressure of the external 

 medium. 



By analysis, it was found that 1.55 per cent of the blood, plasma and 

 corpuscles is urea. This means that the urea constitutes 1.94 per cent 

 of the serum, which is equal to a 0.32 gram molecular solution. Since 

 the freezing point of a gram molecular solution is — 1.84° (Xernst, '09) 

 a 0.32 solution would have a freezing point of about — 0.59°. This 

 amount represents the lowering of the freezing point of the blood due to 

 urea. The salts present in the blood are, however, equivalent to a 0.24 

 gram molecular solution of sodium chloride. This, allowing for dissocia- 

 tion, has a freezing point of — 0.85° '\ This represents the lowering of 

 the freezing point due to the inorganic salts of the blood. The sum of 

 0.59° and 0.85°, or 1.44°, represents the lowering of the freezing point 

 of the blood due to both its urea and inorganic salts. The freezing point 

 of the blood is, however, —1.87°. There is thus left 0.43° to be ac- 



3 As computed from Landolt and Bernstein's Tabellen '05. 



