PHYSIOLOGICAL CHEMISTRY 



acid. The amino acid of this is closely related to leucin. It has 

 recently been shown, however, that the true constitution of leucin 

 is not araino-caproic acid but rather amino-isobutylacetic acid (CH 3 ) 2 : 

 CH . CH 2 . CHNH 2 . COOH. 



EXPERIMENT VI. Examine crystals of leucin under the micro- 

 scope and note that they consist of round balls not unlike oil globules 

 yellowish in colour, and usually having concentric markings (Fig. 236). 



FIG. 23(5. Crystals of leucin and tyrosin. 



Leucin and tyrosin were among the first-discovered composition 

 products of proteins, and, on account of the ease with which they 

 are isolated, they have been detected in nearly every organ and 

 tissue of the body, being probably produced, however, by the chemical 

 agencies employed in examining these, and not existing as such in 

 the living tissue. They also occur, along with excess of ammonium 

 salts, in the urine of patients suffering from severe disease of the liver. 



Not only are amino derivatives of mono-basic acids produced during 

 protein decomposition, but we may also have similar derivatives of 



