508 NUTRITION. 



in Arctic explorations, because the greatest care is always taken to protect the surface 

 of the body as completely as possible ; but experiments have shown that the animal heat 

 may be considerably reduced, as a temporary condition, without producing death. In the 

 latter part of the last century, Dr. Ourrie caused the temperature in a man to fall 15 

 by immersion in a cold bath ; but he could not bring it below 83. This extreme 

 depression, however, lasted only two or three minutes, and the temperature afterward 

 returned to within a few degrees of the normal standard. Nearly the same results were 

 obtained by Hunter, in a series of experiments on a mouse. With an external tempera- 

 ture of 60, he found the temperature in the upper part of the abdomen 99, and in the 

 pelvis, 96. The animal was then exposed for an hour to a cold atmosphere of 13, and 

 there was a diminution of the temperature at the diaphragm of 16, and at the pelvis, of 

 18. These results show that, while the normal variations in the temperature in the human 

 subject, even when exposed to great climatic changes, are very slight, generally not rang- 

 ing beyond two degrees, the body may be exposed for a time to excessive heat or cold, 

 and the extreme limits, consistent with the preservation of life, may be reached. As far 

 as has been ascertained by direct experiment, these limits are 83 and 107; giving a 

 range of about 15 below and 9 above the average standard under normal conditions. 



Variations in Different Parts of the Body. It is to be expected that the temperature 

 of the internal organs should be higher and more constant than that of parts, like the 

 axilla or mouth, more or less exposed to loss of heat by evaporation and contact with 

 the cool air ; and the differences observed in the blood in certain parts, as in the two 

 sides of the heart, have important bearings, as we shall hereafter show, upon the various 

 theories of animal heat. We shall here simply note the variations observed in the blood 

 in different situations and confine ourselves chiefly to late observations, which have gen- 

 erally been made with apparatus much more reliable and delicate than that which was 

 formerly employed. 



A great number of experiments have been made upon modifications in temperature 

 accompanying the general change of the blood from arterial to venous ; but perhaps the 

 most exact and elaborate are those by M. Claude Bernard. For measuring the tempera- 

 ture in different parts of the vascular system, he used the exceedingly delicate " metastatic " 

 thermometers of M. Walferdin ; and in all comparative observations he employed the 

 same instrument, introduced successively into different parts, frequently reversing the 

 order and employing every precaution so as to insure perfectly physiological conditions. 

 The preeminent skill of this distinguished observer in experimenting upon living animals 

 is almost in itself a sufficient guarantee of the accuracy of his results. 



It is universally admitted that the blood becomes slightly lowered in its temperature 

 in passing through the general capillary circulation ; but the amount of difference is ordi- 

 narily not more than a fraction of a degree, and it is dependent, in all probability, upon 

 external conditions and the evaporation constantly going on from the surface of the body. 

 This fact is not at all opposed to the proposition that the animal heat is generated in 

 greatest part in the general capillary system, as one of the results of nutritive action ; for 

 the blood circulates with such rapidity that the heat acquired in the capillaries of the 

 internal organs, where little or none is lost, is but slightly diminished before the fluid 

 passes into the arteries, even in circulating through the lungs ; and the evaporation from 

 the surface simply moderates the heat acquired in the tissues and keeps it at the proper 

 standard. We know that the heat of the body is equalized by means of the circulation 

 and by cutaneous transpiration; and all comparative observations upon the temperature 

 in different parts show that, where it is not subjected to refrigerating influences, the 

 blood is warmer in the veins than in the arteries. 



The elaborate investigations of Bernard have demonstrated that the blood is, as the 

 rule, from 0'36 to 1-8 warmer in the hepatic veins than in the aorta. The tempera- 

 ture in the hepatic veins is from 0-18 to 1'44 higher than in the portal veins. These 



