THE RESPIRATORY SYSTEM. 891 
have been made to determine the pressure relations within an 
alveolus. It is maintained that while the partial pressure of 
the carbonic anhydride rises and of the oxygen sinks, still that 
they remain such as to favor respiration. It is also found that, 
in the asphyxia following occlusion of the trachea, the tension 
of oxygen is always greater, and of carbonic anhydride less, in 
the alveoli than in the blood. On the other hand it is stated 
that oxy-hemoglobin is found in the blood when every trace of 
oxygen is removed from a chamber in which an asphyxiating 
animal is breathing, so that it is argued that partial pressures 
alone can not explain the facts of respiration, and that this 
function is fundamentally a chemical process; and it is cus- 
tomary to speak of the oxygen of oxy-hemoglobin as being in 
a state of “loose chemical combination.” 
The entire truth seems to lie in neither view, though both 
are partially correct. 
The view expressed by some physiologists, to the effect that 
diffusion explains the whole matter, so far, at least, as carbonic 
anhydride is concerned, and that the epithelial cells of the lung 
have no share in the respiratory process, does not seem to be 
in harmony either with the facts of respiration or with the 
laws of biology in general. Why not say at once that the facts 
of respiration show that, here as in other parts of the economy, 
while physical and chemical laws, as we know them, stand 
related to the vital processes, yet, by reason of being vital 
processes, we can not explain them according to the theories of 
either physics or chemistry ? Surely this very subject shows 
that neither chemistry nor physics is at present adequate to 
explain such processes. It is, of course, of value to know the 
circumstances of tension, temperature, etc., under which respi- 
ration takes place. We, however, maintain that these are con- 
ditions only—essential no doubt, but, though important, that 
they do not make up the process of respiration. But, because 
we do not know the real explanation, let us not exalt a few 
facts or theories of chemistry or physics into a solution of a 
complex problem. Besides, some of the experiments on which 
the conclusions have been based are questionable, inasmuch as 
they seem to induce artificial conditions in the animals oper- 
ated upon; and we have already insisted on the blood being 
regarded as a living tissue, behaving differently in the body 
and when isolated from it, so that even in so-called blood-gas 
experiments there may be sources of fallacy inherent in the 
nature of the case. 
