640 THE CONSTANT BODILY TEMPERATURE. [Book ii. 



by which heat would be absorbed and made latent. We find 

 indeed that the blood in the hepatic vein is the warmest in the 

 body. Thus in the dog a temperature of 40-73° C. has been 

 observed in the hepatic vein, while that of the vena cava in- 

 ferior was 38-35° to 39-58, and that of the right heart 37-7. 

 The fact that the blood of the hepatic vein is warmer than that 

 of either the portal vein or the aorta, shews that the increased 

 temperature is not due simply to the liver being far removed 

 from the surface of the body. 



The brain too may be regarded as a source of heat, since its 

 temperature is higher than that of the arterial blood with which 

 it is supplied ; though from the smaller quantity of blood 

 passing through its vessels as well as from the changes in it 

 being less massive, it cannot in this respect compare with either 

 the liver or the muscles as a source of heat to the body. 



The blood itself cannot be regarded as a source of any con- 

 siderable amount of heat, since, as we have so frequently urged, 

 the oxidations or other metabolic changes taking place in it 

 are comparatively slight. The heat evolved by the indifferent 

 tissues such as bone, cartilage and connective tissue, may be 

 passed over as insignificant ; and we cannot even regard the 

 adipose tissue as a seat of the production of heat, since the fat 

 of the fat-cells is in all probability not oxidized in situ but 

 simpty carried away from its place of storage to the tissue which 

 stands in need of it, and it is in the tissue that it undergoes 

 the metabolism by which its latent energy is set free. Some 

 amount of heat is also produced by the changes which the food 

 undergoes in the alimentary canal before it really enters the 

 body. 



Hence, taking a survey of the whole body, we may conclude 

 that since metabolism is going on to a greater or less extent 

 everywhere, heat is everywhere being generated ; but that, 

 looked at from a quantitative point of view, the muscles and 

 the glandular organs must be regarded as the main sources 

 of the heat of the body, the muscles being the more important of 

 the two. 



§ 425. But heat, while being thus continually produced, is 

 as continually being lost, by the skin, the lungs, the urine and 

 the faeces. The blood passing from one part of the body to 

 the other, and carrying warmth from the tissues where heat is 

 being rapidly generated, to the tissues or organs where heat 

 is being lost by radiation, conduction or evaporation, tends to 

 equalize the temperature of the various parts, and thus main- 

 tains a "constant bodily temperature." 



When the production of heat is not great as compared with 

 the loss there is no great accumulation of heat within the body, 

 the temperature of which consequentlv is but slightly raised 

 above that of surrounding objects. Thus the temperature of 



