/ PHYSIOLOGICAL CHEMISTRY. 



compounds was a very important step in the direction of 

 clearing up the constitution of the proteins, inasmuch as some 

 of the simplest of these bodies, the protamines, seem to con- 

 sist almost wholly of the hexones. More will be said about 

 this relation later. The hexones are soluble, crystalline, opti- 

 cally active, compounds. 



LEUCINE, C 6 H 13 NO 2 , a-amino-caproic acid, or a-amino- 

 isobutylacetic acid. This has been already mentioned as 

 found abundantly among the products of protein decompo- 

 sition by other agencies. In some cases it appears to con- 

 stitute 50 per cent of the reaction products, and must there- 

 fore play a very important part in the original complex mole- 

 cule. Leucine is found in several different forms; the com- 

 mon product obtained by acid hydrolysis is right rotating and 

 shows in hydrochloric acid solution [a]^ = -|- 17.3. 



TYROSINE, C 9 H 1:1 NC)3, />-oxyphenyl amino-propionic acid. 

 This appears to be a component part of all the common pro- 

 teins, with the exception of gelatin, and from some of them 

 has been obtained in quantity. As already mentioned this is 

 probably the substance which reacts commonly with Millon's 

 reagent. Tyrosine is but slightly soluble in water, from which 

 it crystallizes in bundles of fine needles. Its solutions are 

 optically active. In presence of hydrochloric acid [a]^ = 

 8 to 15, the rotation varying with the amount of acid. 



GLYCOCOLL OR GLYCINE, C 2 H 5 NO 2 , amino-acetic acid. 

 Obtained abundantly from gelatin and also from other pro- 

 teins. It is very soluble in water to which it imparts a sweetish 

 taste. Insoluble in alcohol or ether. 



ASPARTIC ACID, C 4 H 7 NO 4 , amino-succinic acid. Slightly 

 soluble in water, the solutions being right rotating at the ordi- 

 nary temperature. 



GLUTAMINIC ACID, C 5 H 9 NO 4 , a-aminoglutaric acid. The 

 acid is found in several optical modifications. The common 

 form is but slightly soluble in water and is right rotating. 



PHENYLAMINO PROPIONIC ACID, CgHuNO^phenylalanine. 

 This substance resembles tyrosine closely in structure and 



