Febkvary 17, 1905.] 



SCIENCE. 



245 



piratory ratio has no value as indicating 

 the actual course of respiration, and would 

 separate the taking up of oxygen and the 

 production of carbon dioxid as two proc- 

 esses only indirectly related. 



It is clear that such results as have been 

 cited became difficult to reconcile with the 

 idea that respiration is combvistion, and so 

 an attempt was made to evade the force of 

 the facts, while maintaining the compari- 

 son, by introducing a qualifying term and 

 speaking of respiration as 'physiological 

 combustion. ' This modification, however, 

 blinks the difficulty ; it does not remove it. 



Before passing from this part of my sub- 

 ject I may mention another false concep- 

 tion, which is more or less directly de- 

 pendent on the notion that respiration is 

 combustion. One often finds respiration 

 described as a gaseous exchange— the taking 

 up of oxygen and giving ofE of carbon di- 

 oxid— a trade between the atmosphere and 

 the body. Clearly this is another case of 

 transferring the superficial interpretation 

 of our own physiological processes to other 

 organisms. The exchange that takes place 

 between the tissues and the blood, between 

 the blood and air in the lungs, gives the 

 foundation, and the unessential phenomena 

 of respiration become substituted for the 

 essential. It would be quite as correct to 

 describe photosynthesis as 'an exchange of 

 gases,' for carbon dioxid is taken up and 

 oxygen is eliminated. Yet no one ever 

 thinks so superficially of this process. 



ANAEROBIC RESPIRATION. 



For three quarters of the last century it 

 was supposed that the evolution of carbon 

 dioxid could only occur when free oxygen 

 was available. But in the early seventies 

 Pfliiger discovered what seemed a peculiar 

 form of respiration. He found that a frog 

 put into a vacuum continued to give off 

 carbon dioxid; and presently the same 

 phenomenon was observed by Pfeffer and 



others in plants. So firmly had the con- 

 ception of combustion fastened itself upon 

 physiologists, that when this anaerobic 

 respiration came to be explained, it was 

 supposed that certain molecules of organic 

 matter within the cell gave up their oxygen 

 to others, that they might thus be burned in 

 the body furnace to yield energy. Hence 

 arose the term intramolecular respiration. 



The study of anaerobic respiration, mis- 

 leading as this early interpretation of it 

 was, has thrown in late years a very great 

 light upon normal or aerobic respiration. 

 Here is a process which results in the evolu- 

 tion of energy, and gives rise to one im- 

 portant end-product of aerobic respiration, 

 viz., carbon dioxid ; yet it early became 

 evident that it could not be counted a proc- 

 ess of combustion, at least in any sense in 

 which combustion was then understood. 

 Plainly the changes that were going on 

 within the organism which enabled it to 

 give off carbon dioxid when no free oxy- 

 gen was to be had could only be a rear- 

 rangement of atomic groups within the 

 molecule and the formation of products 

 which were simpler than those from which 

 they arose. 



FERMENTATION. 



The process of fermentation, first thor- 

 oughly explored by Pasteur, whose results 

 have been much extended by the brilliant 

 researches of Hansen and many others, are 

 evidently related to those of respiration by 

 the nature of the end products and the 

 conditions under which the processes occur. 

 Indeed when one compares the end prod- 

 ucts of respiration and of alcoholic fer- 

 mentation he finds them to be identical in 

 all respects. Other sorts of fermentation 

 likewise yield many substances that are 

 found originating in the metabolism of the 

 higher plants. 



We have, then, three modes of energy re- 

 lease, which are evidently closely related 



