164 RESPIRATION 



conditions. It will be remembered that in the apple the for- 

 mation of carbon dioxide in an atmosphere of nitrogen is 

 greater than in air, but in air the only detectable final products 

 are carbon dioxide and water, no other carbon derivative 

 accumulates in the tissues ; it is therefore concluded that some 

 of the intermediate products in the phase C, in the presence of 

 oxygen, undergo an oxidative anabolism and are passed back 

 into the system. 



Of this hypothesis the following are significant : (a) 

 Emphasis is laid on the rate of glycolysis, which is regarded 

 as the common measure of respiration in all conditions. 



(b) Hexoses are not the immediate substrate for glycolysis : 

 they are first converted into the more reactive "hetero hexoses." 



(c) That in the final phase there is an oxidative anabolism. 

 This scheme is an hypothesis based on the observed facts 



of respiration of isolated structures : it includes certain de- 

 ductions which are yet to be proven, a point fully appreciated 

 by its authors. Exigences of space forbid a full consideration 

 of the arguments advanced in its support, even if it were 

 desirable in this general survey ; it may, however, be remarked 

 that Blackman apparently accepts Meyerhof and A. V. Hill's 

 hypothesis that there is a re-oxidation of reduced material. 



The view is generally held that respiration is not a single 

 operation but two groups of events controlled by enzymes, 

 some closely associated with the protoplasm and others in- 

 dependent of the protoplasm and therefore not concomitant 

 with life. The first phase is of the nature of fermentation 

 and the last is oxidative. This is illustrated by the following 

 observations : — 



Palladin and Kostytschev showed that germinated peas 

 which had been killed without injury to the enzymes may give 

 off more carbon dioxide than during life, and so also may the 

 bulb of an onion, killed by exposure to a temperature of — 20° C. 

 on thawing, although in this instance the amount of oxygen 

 absorbed is less than in the living condition. A. R. C. Haas * 

 found that plants of Laminaria poisoned by various substances 

 such as ethyl bromide, acetone, or alcohol first showed a rise 

 * Haas, A. R. C. : " Bot. Gaz.," 1919. 67, 347. 



