BY JAMBS M. PETRIB. 831 



till at last we come to a stop and behold only the familiar mile- 

 stones again ? 



Much new light has been thrown on this region by the exten- 

 sion of Latham's hypothesis(83) as to the synthesis of organic 

 matter in plants. He shows methods of possible genesis of 

 organic compounds from the first products of assimilation, and 

 how by the well known steps of organic chemistry all the con- 

 stituents can be prepared. Let us first consider the earliest 

 stages of the sjmthesis. (1) Carbonic acid is reduced to formic 

 acid, then to formaldehyde; formic acid unites with ammonia 

 ■(absorbed by the roots), and the ammonium formate by dehydra- 

 tion yields hydrocyanic acid. (2) Then by means of aldehydes, 

 hydrocyanic acid, and ammonia, we can obtain amino-acids, 



aldehyde "I — ">cyan-alcohoU — ">amino-nitril I — ">amino-acid 

 + HCN J +N H 3 ) +H 2 i 



Latham regards these cyan-alcohols as the antecedents of the 

 amino-acids in living protein. (3) By starting with acetaldehyde 

 we can also obtain asparagin and arginin; from propionic aldehyde 

 glutamin and lysin can be formed, and from benzaldehyde we 

 can obtain tyrosin. 



These practical methods of the laboratory are of great signifi- 

 cance in that they show us where exist the articulations of the 

 giant protein-molecule. They enable us to perceive how each of 

 the small segments may be utilised as bricks for building; these 

 may, however, not all be necessary in the living organism, for 

 our most perfect synthetic methods are infinitely excelled by the 

 oase with which the catalytic enzymes arrive at the same result. 

 Protein has been decomposed by peptic and tiyptic enzymes to 

 amino-acids (not precipitable by 85 % alcohol); when these were 

 concentrated to incipient crystallisation, and again subjected to 

 the action of the same enzymes, it was found that the original 

 protein was regenerated(102). 



References to Literature. 



1. " Rothamsted Experiments," 1893. 



2. Suzuki— Bull. Coll. Agric. Tokio Univ. vii. 1907, 513. 



3. Winogradsky — Ann. Inst. Pasteur, 1890. 

 -4. Baeyer — Ber. iii., 1870, 66. 



