520 NUTRITION. 



period, 300 parts of blood, with 30 parts of oxygen, pass through, but that the venous blood 

 contains five per cent, of oxygen, or 15 parts. That would show an actual consumption 

 of 15 parts of oxygen in inflammation, against 7'5 under normal nutritive conditions. 

 Estor and Saint-Pierre do not state the amount of increase in the quantity of blood cir- 

 culating through inflamed tissues, but they admit that, " in inflammation, the vessels are 

 dilated, and the current of blood is more rapid." An increase in the absolute quantity 

 of blood passing through parts after division of the sympathetic nerves distributed to the 

 coats of the blood-vessels has been observed by all who have experimented upon the sub- 

 ject ; and the increase is probably greater than that which we have assumed in our argu- 

 ment. An additional argument in favor of our interpretation of the experiments of 

 Estor and Saint-Pierre is the fact, noted by them, that the blood from inflamed parts 

 contains more carbonic acid than ordinary venous blood. 



Taking into account all the facts bearing upon the question, there can be little doubt, 

 that, while the processes of nutrition and disassimilation, involving changes in the nitro- 

 genized constituents of the blood and the tissues, are not disconnected with calorifica- 

 tion, the production of heat by animals is most closely related to the appropriation of 

 oxygen and the formation of carbonic acid. 



Intimate Nature of the Calorific Processes. A comprehension of the intimate nature 

 of the calorific processes involves simply an answer to the question, how far we can fol- 

 low the material transformations in the organism, which involve the consumption of cer- 

 tain principles, the production of new compounds, and the evolution of heat. As regards 

 the nature of the intermediate processes connecting the disappearance of oxygen with 

 the production of carbonic acid, we can only explain it by reciting the simple facts. 

 Oxygen disappears, carbonic acid is formed, and the carbon is furnished, perhaps by the 

 tissues, perhaps by the blood, probably by both. It is probable that the intermediate 

 changes are more simple and rapid than those which intervene between the appropria- 

 tion of nitrogenized nutritive matter and the formation of the nitrogenized excretions ; 

 but we have never been able to follow either of these processes through all of its dif- 

 ferent phases. We must be content, in the present condition of our positive knowledge, 

 to regard calorification as one of the attendant phenomena of nutrition ; and we have 

 only to study as closely as possible the facts with regard to the disappearance of certain 

 principles and the formation of effete matters, that are always and of necessity associated 

 with the development of heat. 



Equalization of the Animal Temperature. A study of the phenomena of calorification 

 in the human subject has shown that under all conditions of climate the general heat of 

 the body is equalized. Nearly always, the surrounding temperature is below the standard 

 of heat of the body, and there is, of necessity, an active production of caloric. Under 

 all conditions, there is more or less loss of heat by evaporation from the general surface ; 

 and, when the surrounding atmosphere is very cold, it becomes desirable to reduce this 

 loss to the minimum. This is done by appropriate clothing, which must certainly be 

 regarded as a physiological necessity. The proper kind of clothing, the conducting 

 power of different materials, their porosity, etc., form important questions in practical 

 hygiene, and their full discussion belongs to special treatises. Clothing protects from 

 excessive heat as well as from cold. Thin, porous articles moderate the heat of the sun, 

 equalize evaporation, and afford great protection in hot climates. In excessive cold, 

 clothing is of the greatest importance in preventing the escape of heat from the body. 

 When the body is not exposed to currents of air, the garments are useful chiefly as non- 

 conductors, imprisoning many layers of air, which are warmed by contact with the person. 

 It is farther very important to protect the body from the wind, which increases so greatly 

 the loss of heat by evaporation. It is wonderful, however, how intense a cold may be 

 resisted by healthy men under proper conditions of alimentation and exercise and with 



