Chemical Constituents of the Animal Body. 223 



CH 

 S \ 



N NH 



= C CH 2 CH(NH 2 ) COOH 

 15. Proline, a-pyrollidinecarboxylic acid 



CH 2 -CH 2 

 H 2 CHCOOH 



^/ 



A 



16. Hydroxyproline, a hydroxyl derivative of the above. 



17. Tryptophan or /3-indole-a-aminopropionic acid 



CH 



C 6 H 4 CH CH 2 CH(NH 2 ) COOH 



HYDROLYSIS OF PROTEINS AND SEPARATION OF THE 

 AMINO- ACIDS PRODUCED IN THIS OPERATION. 



The hydrolysis is generally carried out by means of 

 25 per cent, sulphuric or hydrochloric acid. The protein 

 is first warmed with about three times its weight of the 

 acid on a water bath, and the reaction is completed over a 

 free flame, the flask in which the operation is carried out 

 being provided with a reflux condenser. When sulphuric 

 is employed, it is removed quantitatively at the completion 

 of the hydrolysis (which usually takes about sixteen hours) 

 by the addition of a theoretically requisite quantity of 

 barium hydroxide. After filtration of the barium sulphate 

 thus precipitated, and concentration of the liquid, the 

 greater part of the tyrosine and cystine separate when 

 these substances are present in sufficient quantity. The 

 separation of the monoamino-acids can be effected by the 

 method due to Emil Fischer. The principle consists in 



