208 THE ATMOSPHERE 



grow in media containing neither organic nitrogen or carbohydrate. 

 They are of great theoretical interest, because they build proteid 

 out of inorganic salts (ammonia or nitrites, C0 2 and Na 2 C0 3 , are 

 necessary) without the aid of chlorophyll. It has been demon- 

 strated that the synthesis of plant protoplasm takes place in the 

 green leaves, for the proteid content increases if the leaves of the 

 sunflower are fed with a solution of sugar and potassium nitrate. 

 (This synthesis goes on in the dark.) A purely tentative suggestion 

 has been put forward, that oxy-fatty acids produced from the 

 sugar may unite with ammonia nitrite to form amido-acids, e.g. 

 CH 2 OH . COOH + NH 4 N0 2 - CH 2 NH 2 . COOH + HN0 2 + H 2 0, and 

 that the proteid is formed by the condensation of these amido- 

 acids. The study of the hydrolytic decomposition of proteids 

 and of the products of condensation of amido-acids, such as 

 Grimaux's artificial colloids, has led Hofmeister to the conclusion 

 that proteids are chiefly formed from the condensation of these 

 acids. 



The molecular constitution of the proteids has been studied by decom- 

 posing them by hydrolytic means by boiling mineral acids or by ferments, 

 and also by strong potash, oxidising agents, &c. 



The end products of the relatively most simple proteids consist of a 

 number of carbon nuclei, which are in chemical constitution so far apart 

 from one another that they are regarded as existing preformed in the 

 proteid molecule. 



The nuclei constantly present, according to Hofmeister, consist of 



(1) Nuclei containing C,N,H. Example, the guanidin. radicle CNH . NH 2 . 

 (A group which, on hydrolysis with baryta water, yields urea.) 



(2) Nuclei containing C,N,H,0 



(a) Mono-basic, mono-arnido acids, with the general formula 



CnH 2 n+ 1, N0 2 as leucin (C 6 ), glycin (C 2 ), alanin (C 3 ). 



(b) Dibasic mono-amido acids, C n 13. 2n _ l , N0 4 as glutaminic (C 5 ) 



and asparaginic (C 4 ) acids. 



(c) Mono-basic diamido acids, C w H 2n+2 , N 2 2 as ornithin (diamido 



valerianic acid), argininin (guanidin- amido valerianic acid), 

 lysin (a-e diamido caproic acid). 



(3) Amido-alcohols or hexosamiiies, which yield the carbohydrate group 

 of proteids as chitosamin (C 6 H 13 N0 6 ). A carbohydrate group has been 

 obtained from both serum albumin and globulin, and is probably common 

 to most proteids. 



(4) Nuclei containing C,N,H,0,S, as cystein or amido-thio-lactic acid, 

 CH 2 SH . CH(NH 2 ) COOH. 



