462 ANIMAL HEAT. [BOOK n. 



Next to the muscles in importance come the various secreting 

 glands. In these the protoplasm, at the periods of secretion at all 

 events, is in a state of metabolic activity, which activity as else- 

 where must give rise to heat. In the case of the salivary gland of 

 the dog the temperature of the saliva secreted during stimulation 

 of the chorda has been found to be as much as 1 or 1'5 higher 

 than that of the blood in the carotid artery at the same time, and 

 in all probability the investigation of other' secreting glands would 

 lead to similar results. Of all these various glands, the liver 

 deserves special attention on account of its size and large supply 

 of blood, and because it appears to be continually at work. We 

 find indeed that the blood in the hepatic veins is the warmest 

 in the body. Thus in the dog a temperature of 4073 C. has been 

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

 was 38-35 to 39'58, and that of the right heart 377. 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 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 

 considerable 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 in- 

 different 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 simply 

 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 ali- 

 mentary 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 every- 

 where, 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 in all probability the more important of 

 the two. 



But heat, while being thus continually produced, is as con- 

 tinually 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 



