GENERAL PROPERTIES AND REACTIONS OF PROTEIDS. 39 

 4CHOH+NH 3 = NH 2 .CH.COH+2H 2 



CH 2 .COH 



By polymerisation of aspartic aldehyde we have 



fNH2.CH.COH] 



M | \ = C 12 H 17 N 3 4 +2H,0 



[ CH 2 COHJ 



and by further polymerisation in the presence of a sulphur compound 

 and hydrogen we get 



6C 12 H 17 N 3 4 +H 2 S+6H 2 = C 72 H 112 N 18 S0 22 +2H 2 



which represents the composition of ordinary albumin. If such an 

 aldehyde does exist in " living proteid " its instability is explicable, 

 because molecular movements would be constantly occurring in the 

 aldehyde group. 



The theory is ingenious, but an obvious objection to it is that it assumes 

 the empirical formula above given for albumin to be the correct one. The 

 theory has been adversely criticised by Baumann 1 who points out that alde- 

 hydes are not the only substances that reduce alkaline solutions of silver 

 nitrate, but that many organic substances, such as pyrogallol, resorcin, hydro- 

 chinon, pyrocatechuic acid, alloxan, and morphine do so also. It is stated, 

 moreover, by Kretzschmar 2 and Griffiths, 3 that both living and dead proto- 

 plasm give the reaction. 



Lathams theory* This is to some extent a combination of the two 

 just described. Latham considers living proteid to be composed to a 

 chain of cyanalcohols or cyanhydrins, as they are often called, united to 

 a benzene nucleus. 



A cyanalcohol is a substance obtained by the union of an aldehyde 

 with hydrocyanic acid ; for instance 



CH 3 .COH+HCN=CH 3 .CH(CN)OH 



(ethaldehyde) (hydro- (cyanethylic alcohol) 

 cyanic acid) 



Other alcohols are formed from other aldehydes, and these are all 

 united to one another and to benzene to form a proteid. 



Latham shows that the various products of the disintegration of 

 albumin can also be obtained by the condensation and intramolecular 

 changes that these cyanalcohols, which are exceedingly unstable 

 substances, undergo. Instability and proneness to undergo intra- 

 molecular changes are two properties common to " living proteids " and 

 to cyanalcohols. 



General properties and reactions of proteids. Solubilities. 

 All proteids are insoluble in alcohol and ether. Some are soluble in 

 water, others insoluble. Many of the latter are soluble in weak saline 

 solutions. Some are insoluble, others soluble in concentrated saline 

 solutions. It is on these varying solubilities that proteids are classified. 



All proteids are soluble with the aid of heat in concentrated mineral 

 acids, in glacial acetic acid, and in caustic alkalis. Such treatment, how- 



1 Arch.f. d. ges. Physiol, Bonn, 3882, Bd. xxix. S. 400. 



2 Centralbl.f. agric. C/icm., Leipzig, 1882, p. 830. 



3 Chem. News, London, vol. xlviii. p. 179. 



4 Brit. Med. Journ., London, 1886, vol. i. p. 629; Lancet, London, 1888, vol. ii. p. 751. 



