434 TEXT-BOOK OF PHYSIOLOGY. 



urine and feces during this period were collected and their heat value 

 determined, which amounted to 305 Calories. The heat which theoretic- 

 ally should have been produced was 4119 Calories. During the experiment 

 the calorimeter actually absorbed 3958 Calories, a difference between the 

 theoretic and experimental results of 156 Calories; thus of the total energy 

 liberated 96 per cent, appeared as heat. 



Calorimetric experiments on man corresponding to those made by 

 Rubner on dogs have not been successful, owing purely to technical diffi- 

 culties. Various attempts have been made, however, to determine the daily 

 heat-dissipation. Liebermeister immersed a man in a bath with a tem- 

 perature lower than that of the man's body. From the rise in temperature 

 of the water it was calculated that the man produced daily 3525 Calories. 

 Leyden placed the leg alone of a man in a calorimeter. In one hour 6 

 Calories were absorbed. Assuming that the total superficial area of the body 

 was fifteen times that of the leg, he calculated, taking into consideration 

 various sources of error, that the entire body would produce daily 2376 

 Calories. Ott, employing a water calorimeter, found that the body of a 

 man produced 103 Calories during an afternoon, or at the rate of 2472 Cal- 

 ories daily. These and similar experiments, while not free from many 

 objections, furnish results which indicate that the heat dissipated from the 

 body approximates the physiologic heat values of the foods. 



HEAT -DISSIPATION AND REGULATION OF THE TEMPERATURE. 



Heat-dissipation. From the preceding statements it is evident that 

 the body is continually liberating heat in amounts daily far in excess of 

 that necessary for the maintenance of the body-temperature. Should 

 this heat be retained, the temperature of the body would be raised at 

 the end of twenty-four hours an additional 18 or 20 C. a temperature 

 far in excess of that compatible with the maintenance of physiologic pro- 

 cesses. That the body may be kept at the mean temperature of 37 C. it 

 is essential that the heat liberated be dissipated as fast as it is produced, 

 or to state the problem in another way, the heat dissipated by the body 

 must be replaced by an equal amount liberated, if equilibrium of temperature 

 is to be maintained. The dissipation of the heat is accomplished in several 

 ways: (i) In warming the food and drink to the temperature of the body. 

 (2) In warming the inspired air to the same temperature. (3) In the eva- 

 poration of water from the lungs. (4) In evaporating water from the skin. 

 (5) In radiation and conduction from the skin. The quantities of heat lost 

 to the body by these different processes it is difficult for obvious reasons to 

 accurately determine, and the estimates usually given must be regarded only 

 as approximative. 



Assuming 2500 Calories to be an average of heat liberated during a day 



of repose, the losses, in the ways stated above, may be given as follows: 



i. In Warming Food and Drink. The average temperature of food and 



drink is about 12 C.; the amount of both together is about 3 kilograms; 



the specific heat of food about 0.8 that of water. The absorption 



of body-heat therefore by the food amounts approximately to 3X0.8 



X25 C. = 6o Calories = 2. 8 per cent. With the removal of the end- 



