CHEMICAL BASIS OF THE ANIMAL BODY. 163 



however involve any one of the three following processes. The 

 ammonia may unite with carbonic acid to form ammonium carbonate, 

 which is then dehydrated into urea (Schmiedeberg). Again, it may 

 unite with carbamic acid to form the carbamate which again by loss of 

 one molecule of water yields urea (Drechsel) 1 . But in the third place 

 the ammonia residues may unite with some cyanic compound to form 

 urea in accordance with the possibilities indicated above (pp. 156, 160) 

 (Salkowski and Hoppe-Seyler). The view that some cyanic residues may 

 be involved in the formation of urea, while at present devoid of any 

 striking positive evidence in its support, is at first sight most attractive, 

 especially when it is borne in mind how great the molecular energy of 

 the cyanogen compounds is, so that during their degradation in the 

 tissues much energy would be set free. Pfliiger, 2 following Liebig, has 

 called attention to this great molecular energy of the cyanogen com- 

 pounds, and has suggested that the functional metabolism of protoplasm 

 by which energy is set free, may be compared to the conversion of the 

 energetic unstable cyanogen compounds into the less energetic and 

 more stable amides. In other words, ammonium cyanate is a type of 

 living, and urea of dead nitrogen, and the conversion of the former into 

 the latter is an image of the essential change which takes place when a 

 living proteid dies. 



If we accept this view it is perhaps difficult to understand how 

 the cyanic compounds, poisonous as they are known ,to be, could 

 play a part in the body. But it is apparently the (CN) group which 

 confers on the compounds their poisonous properties ; and if cyanic acid 

 be truly carbamide CO . NH this group is non-existent in it, and it has 

 been recently stated that cyanuric acid (CO . NH) 3 when introduced 

 into the body leads to an increased excretion of urea 3 . 



One difficulty in connection with this view is that as yet cyanic acid has never 

 been obtained by the artificial decomposition of proteids. But on the other hand 

 the proteids are the chief and only source of the cyanogen compounds, for which 

 the starting point is found in ferrocyanide of potassium, prepared by fusing nitro- 

 genous animal refuse with potassium carbonate and iron. There is further evidence 

 of the existence in the body of cyanic residues, as shown by the exit from it of 

 sulphocyanates (HCNS), which are found in both saliva and more particularly in 

 urine 4 . The existence of sulphur in these salts suggests at once that it arises from the 

 decomposition of proteids into whose composition sulphur enters as a constant and 

 characteristic constituent. The -formation of sulphocyanic acid in the body has 

 recently been investigated, and it is worthy of note that it is stated to occur in the 



1 Cf. above sub sarkosin, p. 141, and carbamic acid p. 152. 

 3 Pfliiger's Arch. Bd. x. (1875), S. 337. 



3 Coppola, Rendic. d. R. Ace. d. Lincei, 1889, pp. 378, 668. Ann. di Chim. e 

 difarmac. (4) T. x. (1889), p. 3. 



4 Munk, Virchow's Arch. Bd. LXIX. (1877), S. 354. Gscheidlen, Pfliiger's Arch. 

 Bd. xiv. (1877), S. 401. 



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