ANIMAL HEAT 603 



take the specific heat of blood as about equal to that of water, this 

 represents a heat-production of ^g- x , or 9 calories per hour. 



Now, the total heat-production of a y-kilo dog is about 19 calories 

 per hour, of which somewhat less than one-half is probably formed 

 in the skeletal muscles. 



The blood of the inferior vena cava at the level of the kidneys 

 may be OT colder than that of the abdominal aorta, but is warmer 

 than the blood of the superior cava. The right heart, therefore, 

 receives two streams of blood at different temperatures, which 

 mingle in its cavities. A controversy was long carried on as to the 

 relative temperature of the blood of the two sides of the heart ; 

 but the researches of Heidenhain and Korner have shown that a 

 thermometer passed into the right ventricle through the jugular 

 vein stands, as a rule, slightly higher than a thermometer introduced 

 through the carotid into the left ventricle. They consider that the 

 method gives not so much the temperature of the blood in the two 

 cavities as that of their walls. The thin-walled right ventricle, 

 according to them, is heated by conduction from the warm liver, 

 from which it is only separated by the diaphragm, while the left 

 ventricle loses heat to the cooler lungs. They deny that the differ- 

 ence of temperature is caused by cooling of the blood in its passage 

 through the pulmonary capillaries, for even when respiration is sus- 

 pended, they find a difference of temperature between the two sides 

 of the heart. Under ordinary circumstances, they say, the inspired 

 air is already heated almost to body-temperature before it reaches 

 the alveoli. But, while this is the case, a fall of less than ^"0 m "the 

 temperature of the blood passing through the lungs would account 

 for all the heat lost by the expired air. If half of the loss took place 

 in the upper air-passages, less than ^ would be sufficient. A slight 

 difference of temperature in the blood of the two ventricles might be 

 caused, even in the absence of respiration, by the heat developed in 

 the cardiac muscle itself during contraction, a large proportion of 

 which must be conveyed by the blood of the coronary veins into the 

 right side of the heart. 



The surface temperature varies between rather wide limits with 

 the temperature of the environment. The temperature of cavities 

 like the rectum, vagina, and mouth, and of secretions like the urine, 

 approximates to that of the blood in the great vessels or the heart, 

 and undergoes only slight changes. An increase in the velocity of 

 the blood causes the internal and surface temperatures to come nearer 

 to each other, the former falling and the latter rising. When the loss 

 of heat from a portion of the surface is prevented, the temperature 

 of this portion approaches the internal temperature. For this reason 

 a thermometer placed in the axilla approximately measures the 

 internal temperature, and not that of the skin ; and a thermometer 

 in the groin of a rabbit, and completely covered by the flexed thigh, 

 may stand as high as, or, it is said, even higher than, a thermometer 

 in the rectum (Hale White) . The temperature in the mouth is not 

 a very reliable index of the deep temperature of the body, especially 

 in cold weather or after exercise, as it is apt to be influenced by the 

 inspired air. The mouth must, of course, be kept closed during 

 the measurement. On the average its temperature is about the 

 same as that of the axilla, and o'4 C. below that of the rectum. The 

 rectal temperature is o'2, or 0-3 above that of the urine. In point 

 of accuracy rectal observations are the best, and next to them 

 determinations of the temperature of the stream of urine. The 



