THE MUTUAL RELATIONS. 325 



bination with the relatively large amount of nitrogen. This must certainly 

 possess some deep significance. Let us consider leucine: 



. CH 2 . CH . (NH 2 )COOH, 

 CHs 



and urea: 



c=o 



X NH 2 



The nitrogen united to C = O in the latter compound, is derived from 

 two molecules of monoamino acid. What becomes of all of the rest of 

 the carbon chain? We know nothing about this nitrogen-free residue of 

 the amino acids. It is possible that it is immediately consumed. This 

 has never been satisfactorily proved. On the other hand, we can under- 

 stand the fact that nitrogen leaves the organism in the form of urea, from 

 the standpoint that the organism has utilized the energy of the albumin 

 to the fullest possible extent. An elimination of carbon chains containing 

 nitrogen would indicate an incomplete combustion of available material. 

 The fact that the disintegration of the albumin in this manner is a very 

 economical one, a loss of energy always occurs in the urea itself, does not 

 permit us to form any opinion regarding the utilization of the remainder 

 of the carbon. We call attention to these relations, because the whole 

 question of the relation of albumins to fats and carbohydrates is dependent 

 upon this, and we wish to emphasize the point that the assumption of the 

 albumin being rapidly consumed in toto, is not sufficiently supported by 

 the facts. 



Let us consider those investigations and observations which are held 

 to prove that fat may be produced from albumin. We must state, at the 

 start, that a large number of such investigations are worthless, owing to 

 the fact that the methods employed for estimating the fat do not give 

 any idea as to the actual fat content of any individual organ. The fat 

 in the organs is evidently present in different forms. A part of this may 

 easily be extracted by ether. If we examine a piece of tissue which has 

 been freed of fat in this manner, we obtain the impression that all of the 

 fat has been removed. This is, however, not the case; for if we digest the 

 residue with pepsin-hydrochloric acid, or boil it with 2 per cent hydro- 

 chloric acid, we can extract some more fat with ether. Instead of using 

 ether for extraction purposes, it has been recommended to employ alcohol 

 and chloroform alternately. 1 The fact that the fat is not entirely extracted 



1 C. Dormeyer: Pfliiger's Arch. 65,90 (1897). J. Nerking: ibid. 73, 172 (1898); 

 85, 330 (1901). O. Frank: Z. Biol. 35, 549 (1897). E. Voit: ibid. 35, 555 (1898). 

 E. Bogdanow: Pfliiger's Arch. 86, 389 (1897). G. Rosenfeld: Z. in. Med. 33 (1900). 



