THE CHEMICAL CONSTITUTION OF ITS UNITS 45 



arid Geiger in 1906, and was carried out as follows, starting from chlor- 

 acetal : 



/OC 2 H 5 NaOC 2 H 5 /OC 2 H 5 H 2 O 



C1.CH 2 .CH( > C 2 H 5 O.CH 2 .CH( -> 



\OC 2 H 5 \OC 2 H 5 



Chloracetal Ethoxylacetal 



HCN 

 C 2 H 5 .O.CH 2 .CHO ^ C 2 H 5 .O.CH 2 .CH(NH 2 )CN ^ 



NH 3 

 Ethoxylacetaldehyde Ethoxylacetaldehyde-aminonitrile 



Cone 



C 2 H 5 .O.CH 2 .CH(NH 2 )COOH -> HO. CH 2 . CH(NH 2 )COOH 



HBr 



Ethoxylaminopropionic acid Serine 



Cystine. 



Under the name of cystic oxide, a new species of urinary calculus, 

 this compound was first described by Wollaston in 1810. Lassaigne 

 found it under the same conditions in a dog in 1823. Its presence in 

 the kidney of an ox was shown by Cloetta in 1856, and in the following 

 year Scherer found it in the liver of a patient, who had died of typhoid 

 fever. The name cystine was given to it by Berzelius. Drechsel, in 

 1891, isolated it from horse's liver and in 1896 from a porpoise, and 

 then first regarded it as a normal product of metabolism. In 1890 

 Kiilz obtained cystine by the digestion of fibrin with pancreas, and 

 Emmerling, in 1894, found it mixed with tyrosine which he had prepared 

 by the hydrolysis of horn. An attempt was made by Suter, in 1895, 

 to obtain it from horn, but he could only obtain a-thiolactic acid, and 

 not until 1899 was it shown by K. A. H. Morner to be a product of 

 hydrolysis of this protein, and, in 1901, of other proteins also. His 

 results were confirmed by Embden, who was working independently, 

 and who also obtained cysteine, which is derived from cystine as proved 

 by Patten. 



The earliest analyses of cystine are given by Prout, who overlooked 

 the fact that cystine contained sulphur, the presence of which element 

 was first shown by Baudrimont and Malagutis. Thaulow gave cystine 

 the formula C 6 H 12 N 2 O 4 S, and pointed out that it was one of the few 

 compounds made up of five elements. On account of the uneven 

 number of atoms in its molecule, Gmelin replaced this formula by 

 C 3 H 7 NSO 2 , which formula was confirmed by Grote in 1864, and later 

 by Kiilz in 1884. 



The first investigations on the constitution of cystine are those of 

 Dewar and Gamgee in 1871, who, on treating cystine with nitrous acid, 

 obtained an acid which they thought was pyruvic acid, CH 3 . CO . COOH, 



