82 PHYSIOLOGY 



This substance is very widely distributed throughout the vegetable kingdom and 

 is present in seedlings in very large quantities, as much as 25 per cent, of the dried 

 weight. In plants it apparently serves either as a reserve material or as the form 

 in which the greater part of the nitrogen is conveyed from the reserve organs to be 

 built up into the protoplasm of the growing parts of the plant. 



(3) Diamino-ccids 



Of these two are known, namely, lysine and ornithine. Owing to the 

 presence of two NH 2 groups in their molecule, they possess marked basic 

 characters, and are precipitated from the acid solution obtained by the 

 hydrolysis of proteins on adding phosphotungstic acid. Since lysine, argi- 

 nine, and histidine (another amino-acid which will be described later) all 

 contain six carbon atoms in their molecule, these three bodies were classed 

 together by Kossel as the ' hexone ' bases. Apart however from their high 

 content in nitrogen, the chemical resemblance between these bodies is no 

 closer than between them and the other members of the amino-acid series. 

 Another body isolated by Fischer in small quantities is supposed to 

 belong to this class and to have the composition diamino-trioxydodecoic acid. 

 LYSINE C 6 H 14 N 2 2 is a--diamino-caproic acid having the formula 



CH 2 NH 2 



I 



(CH 2 ) 3 



I 



CH.NH 2 



I 

 COOH 



ARGININE, which was first discovered in plants (the cotyledons of 

 lupins), is not a simple amino-acid, but a compound of an amino-acid with 

 guanidin. If boiled with baryta water it splits up into urea and a substance 

 reacting as a base which was called ornithine.* 



ORNITHINE, diamino-valerianic acid, has the formula 



(CH 2 ) 2 



I 

 CH.NH 2 



I 

 COOH 



The constitution of arginine is analogous to that of creatine, one of the 

 most abundant nitrogenous extractives of muscle, which has the formula 

 HN = C i N(CH 3 )CH 2 COOH 



It is methyl guanidine acetic acid. On boiling creatine with baryta water 

 it takes up a molecule of water and splits in the situation of the dotted line 

 in the formula, giving 



* Ornithine had been previously discovered in the urine of fowls after the adknini- 

 stration of benzoic acid, in the form of an acid known as ornithuric acid, 



