204 METABOLISM 



only partial and reaches the formation of organic acids only and not to the final 

 products, water and carbon-dioxide, although the amount of oxygen necessary 

 to burn the substance completely is without doubt available. A certain light 

 is shed on the cause of respiration by a consideration of intra-molecular respira- 

 tion. If we assume with Pfeffer (1889) that normal and intra-molecular 

 respiration have a genetic connexion, that intra-molecular succeeds normal respira- 

 tion when oxygen is deficient — and this assumption is the most probable that 

 occurs to one — then we are forced to admit the decomposition of organic bodies as 

 the primary phenomenon in both processes. The decomposition must result in 

 the formation of an oxidizable body, which in the presence of free oxygen takes 

 it up, but which in its absence satisfies its requirements so far as oxygen is con- 

 cerned from other compounds containing it. Carbon-dioxide must arise from it in 

 all cases, although the intermediate products must differ according as oxygen is 

 present or not. We must not assume that identically the same products are 

 present in normal respiration as in intra-molecular, and that these, e. g. alcohol, 

 become afterwards oxidized ; that such an assumption cannot be correct is 

 shown by the proportion of carbon-dioxide to oxygen in any selected case. 



It is not known what the bodies are which undergo this hypothetical 

 primary decomposition. They may be the substances which we noted disap- 

 pearing in mass during active respiration, the carbohydrates ; but they may 

 be proteids or even protoplasm itself. The latter view, which has been advanced 

 by Pfluger, and from the botanical side has been vigorously upheld by Detmer 

 (1883), cannot be exactly proved, still one cannot deny its inherent probability. 

 The abundant consumption of carbohydrates would be explained by this theory, 

 for these would serve to regenerate the broken down proteid or protoplasm ; 

 if they be present in insufficient quantity, as in seedlings of Leguminoseae 

 grown in the dark, the regeneration of the broken down proteid is carried 

 only as far as asparagin ; if they be entirely wanting, as in the case of a fungus 

 nourished by peptone only (p. 200), nitrogenous loss takes place, while ammonia 

 is formed. Pfeffer (1885, 656) has, however, advanced a serious objection 

 to this idea, inasmuch as he has shown that intra-moleadar respiration comes 

 at once to an end in the absence of carbohydrates (compare Diakonow, 1886). 



It has recently been suggested that the immediate cause of this supposed 

 decomposition is an enzyme. Hahn (1901) believes he met with such an 

 enzyme in the sap squeezed out of the bulbs of Arum, which caused sugar to 

 disappear without the addition of oxygen. He did not isolate it, however, nor 

 did he examine its properties in detail. On the other hand, in dead plant parts 

 and in expressed sap oxydases have frequently been found, that is, bodies which 

 act as carriers of oxygen and which colour guaiacum resin blue. That these 

 bodies are somehow connected with respiration is not impossible, still proof 

 must be forthcoming that they exist already in the living plant, which is certainly 

 not the case in many. When these bodies have been more fully investigated we 

 shall be in a better position to answer the question as to whether they are to be 

 considered as enzymes and whether they are to be considered as hydrolytic as well 

 as oxidizing. At all events, the mode of action of these two types of enzyme must 

 be fundamentally distinct. The recent literature on the subject of oxydases 

 includes papers by Raciborski, 1898 (a criticism of whose views is given by 

 MoLiscH, 1901; Vines, 1901); Hunger, 1901; Behrens, 1901. [The literature 

 on the subject of the occurrence and function of oxidizing enzymes in the plant 

 has, during the past few years, increased in quantity out of all proportion to the 

 finality and clearness of the explanations offered. We may refer to Czapek, Bio- 

 chemie, II, 464-481, as also to Chodat and Bach (1904) and Raciborski (1905).] 



Respiration is, as already stated, a process of universal occurrence in 

 organisms, one too which is absolutely essential, since when it ceases and, 

 generally speaking, when also oxygen is withdrawn, the more important functions 



