684 ANIMAL HEAT 



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 formed 

 in the skeletal muscles. '' 



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

 be 0-1 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 tem- 

 perature 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 ventriele. 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 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. The difference of temperature is not caused by 

 cooling of the blood in its passage through the pulmonary capillaries, 

 for even when respiration is suspended, a difference of temperature 

 between the two sides of the heart is found. Under ordinary circum- 

 stances, 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 j^ in 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 suffi- 

 cient. A slight difference of temperature in the blood of the two ven- 

 tricles might be caused, even in the absence of respiration, by the heat 

 developed in the cardiac muscle itself during contraction, a large pro- 

 portion of which must be conveyed by the coronary veins into the right 

 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, approxi- 

 mates to that of the blood in the great vessels or the heart, and under- 

 goes nly 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 temperatupe. 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 0-4 C. below 

 that of the rectum* The rectal temperature is 0-2 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 latter method, although subject to obvious limitations, is rapid and 

 free from the danger of conveying infection to the person (Pembrey) . 



The surface temperature is a rough index of the rate of heat-loss; 

 the internal temperature, of the rate of heat-production. A normal 

 skin temperature and a rising rectal temperature would probably in- 

 dicate increased production of heat ; an increased rectal temperature, 



