1905] BARNES—THE THEORY OF RESPIRATION 87 
the taking up of oxygen and the production of carbon dioxid as 
two processes, only indirectly related. 
It.is clear that such results as have been cited became difficult 
tito reconcile with the idea that respiration is combustion, and so an 
attempt was made to evade the force of the facts, while maintaining 
the comparison, by introducing a qualifying term and speaking of 
respiration as ‘‘ physiological combustion.” This modification, how- 
ever, blinks the difficulty; it does not remove it. 
Before passing from this part of my subject I may mention another 
false conception, which is more or less directly dependent on the 
notion that respiration is combustion. One often finds respiration 
described as a gaseous exchange—the taking up of oxygen and 
giving off of carbon dioxid—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 organ- 
isms. 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 photo- 
synthesis 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. 
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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 PrLicER 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 conception 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, misleading as this early 
\nterpretation of it was, has thrown in late years a very great light 
