104 RESPIRATION 



prochromogens, which may be glucosidal in nature ; these pro- 

 chromogens are converted by enzyme action into chromogens. 

 The chromogens are oxidized by peroxidase into respiratory 

 pigment, which oxidation, according to Combes,* is accom- 

 panied by an increase in the respiration intensity. These 

 respiration pigments are the hydrogen acceptors and act in 

 the same way as does the methylene blue in the experiments 

 previously mentioned (p. 64) : they combine with the hydro- 

 gen to reform the chromogen ; the chromogen in turn and by 

 the aid of oxidase combines with atmospheric oxygen to form 

 water, which is thus of aerobic origin, and respiration pigment. 



It will be observed that the views of Palladin and Wieland 

 are in accordance in their regarding hydration an initial change 

 in the oxidation of an aldehyde or a sugar. But to what ex- 

 tent Palladin's ideas regarding the cycle of changes involved 

 in the complete respiratory process are accepted is a matter 

 for individual judgment. His thesis is bound up with Bach 

 and Chodat's hypothesis, the tenability of which is discounted 

 by the observations of other investigators. The respiratory 

 chromogens may act in the way outlined ; but to what extent 

 their operation is universal is very doubtful. The existence of 

 phases, expressed in the different origins of carbon dioxide, 

 appears to be well supported by the facts, as also is the initial 

 hydration phase in certain oxidations. Finally, the occurrence 

 of a fermentation stage in the respiration cycle is a strong pro- 

 bability if not a completely proven fact. 



With regard to the consumption of fats and proteins in 

 respiratory processes, there is but little precise information. 

 Oparinf has examined chlorogenic acid, C 32 H 38 O 19 , which he 

 has found to occur in over a hundred different plants, and finds 

 it to be a substance which readily oxidizes in the air, losing 

 4 atoms of hydrogen and forming a green pigment. The 

 latter can act as a hydrogen acceptor and so act as an oxidiz- 

 ing agent. The calcium salt of the fully oxidized acid is re- 

 presented by the formula CaC 32 H 32 O 19 + 2H 2 O, whilst the 

 salt of the unoxidized acid has the formula CaC 22 H 36 O 19 + 

 2H 2 O. Chlorogenic acid is more particularly active in the 



* Combes: " Rev. gen. Bot.," 1910, 22, 177. 



fOparin: " Biochem. Zeitsch.," 1921, 124, 90; Gorter : " Annalen d. 

 Chemie.," 1908, 359, 217. 



