1905] BARNES—THE THEORY OF RESPIRATION 95 
| for the formation of CO, whether in aerobic or anaerobic respiration. 
Thus several independent observers are testifying to the rather 
widespread occurrence of an enzyme which brings about a disruption 
’ of plant substance, under most varied external conditions, whether 
; the plant be fed on one food or another,'® this dissociation resulting 
| in the formation of carbon dioxid and of various other products. 
THE MECHANISM OF RESPIRATION. 
Let us now focus the light coming from the chemistry of proteids, 
the mechanism of combustion, and the physiology of respiration, to 
form a picture of what goes on in the body. 
First: We should conceive of the respiratory dissociation as taking 
place in the living material of the body and not in a food still unassimi- 
lated. Experiments with a wide range of foods have shown that 
they affect the intake of oxygen and the output of carbon dioxid in 
the most diverse ways, whence it has been assumed that the respira- 
tory ratio varies because of the way in which the given food is oxidized. 
I do not say that it is not possible for the protoplasm to decompose a 
sugar directly or to oxidize a fat. But it must be remembered that 
in no case has it been experimentally proved that the food is directly 
attacked, and that all the facts can be explained on the other assump- 
tion, and some of them very much better than on the theory of direct 
oxidation. Moreover, the lability of proteids which have been raised 
to the life-level is their most striking characteristic as contrasted 
with their ordinary stability. 
In such labile material the second step is easily conceivable. 
There occurs a shifting of the atomic groups within the molecule, 
perhaps as a result of the last step in their anabolism—the addition 
of hydroxyl groups from the water everywhere present. Dissocia- 
tion follows necessarily; very slow perhaps at ordinary temperatures 
and with a scanty supply of water, yet sufficient evidently for the 
maintenance of life. Such conditions may very well be those obtain- 
ing in resting organs, spores, and seeds. But normally this cleavage 
May go on at a measurable rate, without anything more than the 
*9 See a paper is capes which has just come to hand (Ueber die normale 
und die anaerobe Atm g bei Abwesenheit von Zucker. Jahrb. Wiss. Bot. 40:563- 
592. 1904), showing Tas erroneousness of DIAKONOW’s idea that anaerobic respira- 
tion is only possible when sugar is supplied. 
