7 6 



PHYSIOLOGICAL CHEMISTRY 



CH 2 -S S-CH 2 



I 

 CH-NH 2 CH-NH 2 . 



I I 



COOH COOH 



FIG. 25. TYROSINE. 



Cystine is the principal sulphur-containing body obtained from the 

 decomposition of protein substances. It is obtained in greatest amount 

 as a decomposition product of keratin-containing tissues as horn, hoof, 



FIG. 26. CYSTINE. 



and hair. Cystine occurs in small amount in normal urine and is 

 greatly increased in quantity under certain pathological conditions. It 

 crystallizes in thin, colorless, hexagonal plates which are shown in Fig. 



