ANIMAL HEAT. 303 



were performed with much accuracy. The animals were inclosed in a 

 copper cage, through which ventilation was kept up at a known rate, 

 the temperature of the incoming and outgoing volumes of air being noted 

 at intervals of ten minutes. The cage containing the animal was sur- 

 rounded by a known volume of water, at from 26.5 to 29, and the 

 whole apparatus inclosed in an outer case made as nonconducting as 

 possible ; the quantity of heat actually lost from it by external cooling 

 being determined by preliminary observations. The internal tempera- 

 ture of the animal having been taken, he was introduced into the cage 

 and allowed to remain there a certain time. The heat produced within 

 this time was mainly ascertained by the increase of temperature in the 

 water surrounding the cage, the result being corrected by that of the 

 air used for ventilation, as well as by the variation in temperature of the 

 animal himself, and the loss from the apparatus by external cooling. 

 By this method the experimenter found, as the average result of five 

 observations, that a dog of 5.392 kilogrammes' weight, at rest and in 

 the fasting condition, produced in one hour 12.63 heat units; that is, 

 2.34 heat units for every kilogramme of bodily weight. According to 

 these experiments, the heat-producing power in the dog and that in the 

 human subject are nearly the same; while that of the dog is rather the 

 more active of the two. 



Normal Variations of Temperature in the Living Body. The tem- 

 perature of the body is not the same in its different regions, but increases 

 for a certain distance, from the exterior toward the central parts. This 

 is because the living body is subjected to a constant loss of heat from 

 the surface, like any other solid substance of higher temperature than 

 the surrounding air. Consequently the integument and the parts im- 

 mediately subjacent to it, being more exposed to this cooling influence 

 than the internal organs, have habitually a temperature slightly below 

 that of the body in general. Accordingly, whenever the external air 

 rises to the neighborhood of 3t or 3f.5 it feels uncomfortably warm ; 

 because, although this is exactly the normal temperature of the blood 

 and the internal organs, it is considerably above that of the skin, which 

 is readily sensitive to variations of cold or warmth. The cooling influ- 

 ence of the external atmosphere upon the skin is considerably moderated 

 by the movement of the circulation ; since the warmer blood coming 

 from the internal parts constantly supplies the integument with fresh 

 quantities of heat and thus tends to compensate for its external loss. 



Notwithstanding this compensation, however, the difference in tem- 

 perature between the external and internal parts of the body is always 

 perceptible during health. If the bulb of a thermometer be held for 

 some minutes between the folds of skin in the palm of the hand, it will 

 stand at 36.4 ; in the axilla, at 36.6 ; under the tongue, it will reach 

 37.2; in the rectum, 31.5; and Dr. Beaumont found, in the case of 

 Alexis St. Martin, that the thermometer, introduced into the stomach 

 through the gastric fistula, often indicated a temperature of 31.8. It 

 is evident therefore that, in order to ascertain the real internal tempera- 



