GENERAL PROPERTIES AND REACTIONS OF PROTEIDS. 39 
4CHOH+NH 3 = X 1 1 .,CH.COH+2H 2 
CH 2 .COH 
By polymerisation of aspartic aldehyde we have — 
ixiu'iiroin 
3 J I - =C 12 H 17 N 3 4 +2H 2 
I CTLCOIlJ 
and by further polymerisation in the presence of a sulphur compound 
and hydrogen we get 
(X V.H 17 N 3 4 +H,S+6H 2 = C , 7 ,H 11 ,X 1 ,SU :S2 +2H 2 
which represents the composition of ordinary albumin. It 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. 
Latham's theory. 4 — 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./, d. ges. Physiol., Bonn, 1882, Bd. xxix. S. 400. 
- Centralbl. f. ar/ric. ('hum., Leipzig, 1882, p. S30. 
;; Ohem. News, London, vol. xlviii. p. 179. 
4 Brit. Med. .fount., London, 1886, vol. i. p. 629; Lancet, London, 1SSS, vol. ii. p. 7f>l. 
