1910.] 



Blood in Vertebrates and Invertebrates. 



617 



— 0-68° was, therefore, due to urea, which must, consequently, be present to 

 the amount of 218 per cent.* 



The amount of urea in the blood serum of the dogfish was determined. 

 The material which served for this purpose was that, portions of which had 

 been used for the inorganic analyses detailed above. The serum had been 

 preserved with thymol and was in good condition. Weighed quantities were 

 mixed each with five times its volume of absolute alcohol, and the mixture 

 held in a bottle placed in an agitator which was kept in motion for 24 hours. 

 It was then filtered, the precipitate on the filter washed with absolute alcohol, 

 and the combined filtrate and washings, after the volume was accurately 

 ascertained, used for the determination of the urea. The method employed to 

 this end was that of Folin and consisted in heating a measured quantity of the 

 extract with magnesium chloride and hydrochloric acid for two hours, then 

 adding strong alkali and distilling the liberated ammonia into standard acid 

 solution, which was subsequently titrated with standard alkali. By this 

 method the urea in four determinations as calculated from the ammonia 

 found was: 1'965, 2*107, 2'017, and 2"017 per cent. The mean of these was 

 2-026 per cent. 



This would give in the serum a lowering of the freezing point amounting to 

 0'63° The latter with the amount of the depression due to the inorganic 

 salts in the serum would total — 1'7037°. As the A of serum is —2-035° 

 there still remains —0-332° to be accounted for. 



This is due to ammonia salts; although only infinitesimal traces of these 

 were present in the alcoholic extract of the serum yet ammonia compounds 

 were found in considerable amount in the serum itself. The explanation for 

 this is that concentrated alcohol does not dissolve readily certain of the salts 

 of ammonia, notably the phosphate,! and consequently, absolute or concen- 

 trated alcohol may be used to separate the urea and the ammonia salts in the 

 blood. 



The amount of ammonia in the serum of the dogfish was determined with 

 the Folin method and the results of three estimations gave each 0-1727 per 

 cent, of NHg, or a concentration slightly greater than N/10. This would 

 fully account for the depression —0-332°. 



The high ammonia content, the extraordinary concentration of urea and the 

 high percentage of salts, namely 1-7739, in the serum of the dogfish, all are 

 the results of the action of the osmotic pressure of sea water on the blood of 

 the dogfish, not for one or two geological ages but for all the time which has 



* Assuming that a gi^amme-molecular solution gives a A of - TST". 

 t Erwin Herter (' Mitth. Zool. Stat, zu Neapel,' vol. 10, p. 342) found the ui-ine of 

 Scyllium caiulus rich in ammonia and P^O; and it was markedly acid. 



