CHEMICAL CHANGES 105 



oxidation of natural amino acids, peptides and peptones 

 giving origin to ammonia, carbon dioxide, and an alde- 

 hyde. 



R . CH . NH 2 . COOH + O -> R . CHO + NH 3 + CO 2 



The process is accelerated by the presence of certain reagents 

 such as phosphoric acid. Chlorogenic acid would therefore 

 appear to be a respiratory pigment in the sense used by 

 Palladin. 



The chemical changes involved in the destruction of re- 

 spirable material, must be to a large extent conjectural until 

 precise knowledge is available of the relatively simple enzymic 

 and the more complicated protoplasmic agencies employed, 

 and of their mode of attack. For this reason it is desirable on 

 the present occasion merely to give a brief statement of the 

 more obvious possibilities. 



If the essential part of respiration, that concomitant with 

 life in distinction to that post mortem, is essentially anaerobic 

 and there is much to be said for the thesis then a sequence 

 of chemical changes similar to, if not identical with, alcoholic 

 respiration is indicated. Unfortunately agreement regarding 

 the stages in this sequence has not been reached,* although 

 the views of Neuberg and Reinfurth appear to be well sup- 

 ported by the facts of laboratory experiment. According to 

 these views, glucose is converted into glyceric acid and di- 

 hydroxyacetone, each of which yields methyl glyoxal which in 

 turn gives origin to pyruvic acid. The pyruvic acid by the 

 action of carboxylase gives rise to carbon dioxide and to acetic 

 aldehyde, from which ethyl alcohol results. Alcohol is an end 

 product of anaerobic respiration and its fate depends on whether 

 or not an aerobic phase follows. In the presence of oxygen, 

 the alcohol is oxidized to carbon dioxide and water, or it may 

 be used up in the synthesis of protein, since by oxidation it can 

 give origin to acetic acid which is employable in the formation 

 of amino acids. To what extent these intermediate products 

 obtain in the plant is not known and again it must be men- 

 tioned that the plant is not a test tube. Indications of the 

 sequence may possibly be obtained from animal sources and in 

 their respiration glucuronic acid occurs and also lactic acid 



*Vol. I., p. 382. 



