RESPIRATION 203 



for example, breaks down and all the oxygen present becomes used up in the forma- 

 tion of carbon-dioxide there remains over, besides carbon-dioxide, a completely 

 reduced body composed of carbon and hydrogen ; if all the oxygen be not so 

 used up, a body poor in oxygen as compared with glucose is formed, such as 

 alcohol, which, as a matter of fact, always appears in intra-molecular respiration, 

 and which collects often in considerable quantities (Lechartier and Bellamy, 

 1874, Maze, 1900). Thus Brefeld (1876) found | per cent, of alcohol in the 

 leaves of ivy and Corylns after seventeen days ; in grapes, after several weeks, 

 J-2 per cent.; in cherries, after four weeks, I-8-2-5 percent.; and in pea-seedlings, 

 after three months, as much as 5 per cent. [According to Dude (1903, Flora, 

 92, 205) the plants used by Brefeld, at least partly, can withstand the with- 

 drawal of oxygen for only a very short time (hours or days). Matruchot and 

 Molliard (1903) have shown that alcohol is formed by higher plants when 

 micro-organisms are completely excluded. In Lechartier and Bellamy's 

 experiments Fungi or Bacteria doubtless co-operated in bringing about 

 the result.] If seeds of Vicia jaba are kept for two days under water one can 

 recognize the presence of alcohol by the smell on rubbing. In addition to 

 ethyl-alcohol other substances also appear during intra-molecular respiration, 

 i. e. higher alcohols, acids, aromatic compounds, and even hydrogen, but as to 

 their proportional amounts nothing is known. By means of such special 

 decompositions of organic substance the plant parts remain long alive, the 

 most resistant, it maybe, for months, while others die in a few days or hours ; the 

 amount of carbon-dioxide produced is also, as might be expected, very variable, and 

 in extreme cases maybe seven to ten times the volume of the plant part concerned. 



These last-mentioned phenomena, more especially, throw considerable light 

 on the problem of the factors concerned in respiration [compare Barnes, 1905]. 

 We have described respiration as a case of comhustion, and this we were very well 

 entitled to do from the products it gives rise to ; one may arrive easily, however, 

 at a totally incorrect conception of the causes of respiration by such a mode of 

 expression. In ordinary combustion an oxidizable body is oxidized, during 

 which process it absorbs the oxygen of the air, and this combustion may go on 

 at normal or at supernormal temperatures. Physiological combustion or respira- 

 tion takes place at temperatures so low that a direct union between sugar, 

 starch, &c., and oxygen is inconceivable. Further, the oxygen cannot be the 

 cause of the oxidation, since, necessarily, an alteration in the intensity of 

 respiration should be observed simultaneously with an alteration in the amount 

 of oxygen present in the cell, which, as we have already said, is not the case. 

 Further, we have seen that respiration is within wide limits independent of the 

 amount of materials capable of being oxidized, and hence we must also conclude 

 that this is not the cause of physiological combustion. Should we thus be driven 

 to assume the presence in the protoplasm of a substance which can oxidize more 

 vigorously than ordinary oxygen, viz. the so-called ' active oxygen ', we find 

 ourselves at the same time face to face with a serious difficulty. ' Active oxygen ' 

 once present must attack all oxidizable bodies in the plant, whilst it is character- 

 istic of respiration that only some substances are oxidized. It is difficult to see 

 how the cell-wall could resist the attack of ' active oxygen ' if sugar and starch 

 be oxidized by it. Further, Pfeffer (1889) succeeded in bringing direct evi- 

 dence against the occurrence of vigorously oxidizing substances in the cell. He 

 showed that one might introduce into the cells of many plants dilute solutions 

 of peroxide of hydrogen without injuring them, and that the colouring bodies 

 occurring naturally in the plant, as well as chromogenic substances artificially 

 introduced, suffer a change of colour which does not take place in nature. 



If further proof be necessary that physiological combustion is not so 

 simple as ordinary combustion we need only refer to the facts stated 

 above, which show that not infrequently in respiration combustion is 



