Cold or decreased temperature, below a given standard, which for sake of comparison we may take at a mean of 40 deg.  Fahr., reduces this combination of oxygen and carbon in blood.  In my Lettsomian lectures to the Medical Society of London, delivered in 1860, I entered very fully into this subject, and illustrated points of it largely by experiment.  Since then I have done more, and although I have not time here to state the details of these researches, I will epitomize the principal facts.  I found then that, by exposing blood in chambers into which air can pass in and out, the blood could be oxidized at temperatures of 70 deg. if the distribution of air and blood were effectually secured, and I also found a proper standard of oxidation from a proper temperature.  Afterward I proceeded to test for combination at lower temperatures, and discovered a gradually decreasing scale until I arrived at 40 deg.  Fahr., when efficient combination ceased.  Of course, my method was a very crude imitation of nature, but it was sufficient to show this fair and reliable result, that the oxidation of blood decreases as the temperature of the oxygen decreases.

From this point I went to animal life itself.  I exposed animals to pure cold oxygen and to cold atmospheric air, and compared the results with other experiments in which animals of similar weight were exposed to warm air and warm oxygen.  The facts gleaned were most important, for they proved conclusively that the products of combustion, that is to say, the products resulting from the union of oxygen and carbon, were reduced in proportion as the temperature of the oxygen was reduced.  In the course of this inquiry another singular and instructive fact was elicited.  It has been long known that at ordinary temperature, say 60 deg., pure neutral oxygen does not support animal life so well as oxygen that is diluted with nitrogen.  In the nitrogen the molecules of oxygen are more freely distributed under the influence of motion, that is the meaning of the observed fact.  What, then, would be the respective influence of low and high temperatures on the respiration of pure oxygen?  To settle this question, animals of the same size and weight were placed in equal measures of oxygen gas and common air at a temperature of 30 deg.  Fahr., and with the inevitable result that the animal in the pure oxygen ceased to respire one-third sooner than did the animal in common air.  Carrying the inquiry further, I found that if the oxygen gas were warmed to 50 deg.  Fahr., the respiration was continued six times as long as in the previous experiment, while if the warming were carried to 70 deg., it was sustained twenty-four times as long.  I reversed the experiment; I made oxygen with cold produce anaesthetic sleep in a warm-blooded animal.

I need not carry this argument further; it is the easiest of the demonstrative facts of physiological science that reduction of temperature lessens the combining power of oxygen for blood, and therewith causes a reduction of animal force, and a tendency to arrest of that force, which, in the end, means death.