326 EFFECT OF CHEMICAL AGENTS [Ch. XI 



radical HO- is -usually easily released, consequently we find 

 compounds containing this radical in general more assimilable 

 than allied compounds in which the HO- is replaced by H. 

 Especially is this true when the HO- is joined with radicals 

 containing carbon and hydrogen atoms. For example, foods 

 with the radical -CHg • OH are more nutritive than those with 

 -CHg. Hydroxylized acids are better food for bacteria than 

 non-hydroxylized — lactic acid, CgHgOg, is better than pro- 

 pionic acid, CgHgOg. It is, perhaps, a special case under this 

 rule that multivalent alcohols — i.e. those containing several 

 HO groups — are better foods than the univalent ones ; for 

 instance, glycerine, CHjOH-CHOH-CHgOH, is better than 

 propylalcohol, CHg • CHg • CHgOH. Finally, the entrance of 

 the extremely unstable aldehyd (-CH:0) and keton (-CO-) 

 groups increases the nutritive capacity of the food ; for 

 example, glucose, CHjOH • (CH • OH)^CHO, or fructose, 

 CH3OH . (CH . 0H)3 • CO ■ CHjOH, is better than mannit, 

 CH2OH . (CH ■ OH)^- CH2OH. But all substances containing 

 the group CHOH are good foods, since this compound can be 

 used directly in the construction of carbohydrates, and eventu- 

 ally of albumen. 



As an example of the application of these general principles 

 may be given this series of substances arranged in the order of 

 their decreasing nutritive value for yeast and molds (Nagbli 

 and LoE"sv, '80) : 1, sugars ; 2, mannit, glycerine, the carbon 

 groups in leucin ; 3, tartaric acid, citric acid, succinic acid, the 

 carbon groups in asparagin ; 4, acetic acid, ethylalcohol, kinic 

 acid ; 5, benzoic acid, salicylic acid, the carbon groups in pro- 

 pylamine; 6, the carbon groups in methylamin, phenol. 



In conclusion may be mentioned a food for bacteria which, 

 although inorganic, resembles organic compounds in that it 

 may serve as a source of energy. This is the hydrogen disul- 

 phide employed by the sulphur bacteria and allied forms 



(WlNOGRADSKY, '87, '89). 



h. Green Plants. — It has already been shown that organic 

 compounds can be assimilated by green plants. The experi- 

 ments Avhich have shown this have been made upon both algae 

 and phanerogams, especially by Bokoeny, Loew, A. Meyer, 

 and Laueent. It appears that, in the absence of carbon 



