THE CHEMICAL CONSTITUTION OF THE UNITS 105 



Baumann and Preusse's investigations in 1881 upon the fate of 

 bromobenzene in the animal body, though they only constituted in- 

 direct evidence in regard to the constitution of cystine, were of great 

 importance, as they were carried out at the time when cystine was a 

 very scarce compound and only obtainable from calculi. They found 

 that, when bromobenzene was given to animals, it was excreted in the 

 urine in combination with a sulphur-containing compound, which 

 combination had the formula C n H 12 BrSNO 3 , and in this they were 

 confirmed by Jaffe. When boiled with hydrochloric acid, this com- 

 pound was converted into acetic acid and a substance C 9 H 10 BrNSO 2 , 

 from the empirical formula of which Baumann and Preusse supposed 

 that it was cystine C 3 H 7 NSO 2 , in which one of the hydrogen atoms 

 was replaced by C 6 HJBr. Their further experiments led them to the 

 conclusion that it was really a derivative of cystine. On decomposi- 

 tion by alkali, this latter compound yielded bromophenylmercaptan, 

 ammonia and another substance, which they eventually recognised 

 must be pyruvic acid. It had been shown that Dewar and Gamgee's 

 formula for cystine, which was also based upon the formation of 

 pyruvic acid, was not accurate, so they proposed the following : 



xNH 2 /NH 2 .NH.CO.CH, 



CH 3 . C SH CH 3 . C S(C 6 H 4 Br) CH 3 . C S(C 6 H 4 Br) 



\COOH \COOH \COOH 



For cystine For bromophenylcystine For bromophenylmercapturic 



acid 



Baumann next found that cystine, on reduction with zinc and 

 hydrochloric acid, was converted into a new base, which he called 

 cysteine ; this gave the same products on decomposition as cystine, 

 into which it was easily reconverted by oxidation. He therefore recog- 

 nised that these compounds were related to each other, as a mercaptan 

 is to a disulphide ; consequently the formula 



CH 8 .C SH 



\COOH 

 was really that of cysteine, and that of cystine was 



C . S S . C . CH 3 



\COOH 



the former bromophenylcystine being bromophenylcysteine, etc. 



The actual formation of pyruvic acid from various mercapturic acids 

 upon which these formulae for cysteine and cystine were founded, was 

 only shown later by Baumann' s pupils, Konigs, Brenzinger and Schmitz, 



