NORMAL RESPIRATION AND INTRAMOLECULAR 
RESPIRATION. 
GEORGE JAMES PEIRCE. 
“ RESPIRATION is essentially the intake of oxygen and the 
output of carbon-dioxide by living cells. In the higher animals 
two phases of respiration are distinguished — the erternal, the 
exchange of gases between the air or water and the blood; and 
the zzzerzal, the exchange between the blood, lymph, and the 
tissues"! In plants there is, for the most part at least, only 
the one phase, the exchange of gases between the air or water 
and the cells composing the tissues, an exchange which is 
direct and “external,” since it takes place in most cases 
between the air, whether in the intercellular spaces within the 
plant, or unconfined and outside the plant body, and the indi- 
vidual cells. Even in the densest tissues, within which the 
intercellular spaces are small, it is likely that the cells take in 
free oxygen and give out carbon-dioxide, if not directly from 
intercellular spaces, then from their neighbors bordering on inter- 
cellular spaces. In any case, and in every stage of the process 
of respiration except the purely mechanical ones, of which only 
the higher animals are capable, the exchange of gases between 
the cells and the air takes place in solutions, the oxygen enter- 
ing and diffusing through, the carbon-dioxide passing out from, 
the cells only when these gases are dissolved in water. 
The object of respiration in plants is not the maintenance 
of a certain body temperature, together with the production of 
energy needed for doing work, as in warm-blooded animals. 
It is merely the production of energy for doing work, as in 
cold-blooded animals. The average body temperature of plants 
I$, in general, nearly the mean daily temperature of their envi- 
ronment. It will vary within certain limits, the variation being 
i Pembry, M. S. Chemistry of Respiration, Schifer’s 7ext-Book of Physiology, 
vol. i (1898), P. 692. 
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