210 
FREDERICK BARRY 
in those reactions which possess the greater present interest are, on the 
other hand, often very small; so that the corresponding temperature 
coefficients are comparatively slight. Such is the character, for 
instance, of reactions between electrolytes in aqueous solution. 
Finally, in many important types of reactions, the heat evolved is 
itself so small that until very recently it has certainly not been meas- 
urable, although in some instances calculable. Such are dilutions, 
saponifications and hydrolyses, fermentations — reactions of the great- 
est interest to the physiologist. Considering, then, that the tempera- 
ture coefficients of nearly all reactions which take place within the 
living organism are small, and considering also the relatively narrow 
temperature ranges within which life can exist, it is readily seen that 
this effect of temperature, in changing the internal energies of the 
substance which compose the cell, is very small indeed. The influence, 
nevertheless, is by no means negligible. It will be shown in the sequel 
that the shifting of all chemical equilibria is directly dependent upon 
the change in internal energy that accompanies reaction. While 
therefore the primary effect of this change, namely the release or 
absorption of small quantities of heat, may have a relatively slight 
influence in determining the character of the reactions which take 
place, it ma}^ at the same time cause marked changes in the relative 
speeds of these reactions. Such effects will undoubtedly have an 
influence upon the character of such metastable systems. More- 
over, in view of the extreme complexity of physiological reactions, 
particularly with respect to their dependence upon surface adsorption, 
and enzymotic catalysis, and in consideration of the degree to which 
such phenomena are influenced by slight changes in temperature, 
especially in the presence of dissolved electrolytes, it would be a 
reckless statement to make off hand that the primary influence is 
itself in any sense negligible. 
It cannot now be doubted that the law of the conservation of 
energy, from which all the general statements here made may be 
derived, applies to vital as to other processes. The significant and 
convincing work of Atwater, who in a series of exhaustive calorimetric 
tests measured the total energy changes in the human body at work 
and at rest over long periods of time, demonstrated this conclusively.^ 
^ In Atwater's experiments, the heat evoh'-ed by the human b'ody at rest and at 
work was measured — the subject remaining within a sensitively regulated calorimeter 
for several hours in each experiment — while at the same time, the weights of the 
