1100 ANIMAL HEAT 



a grating of lead-paper or tinfoil which is arranged vertically in a 

 closed box to protect it from air-currents. When the observation is 

 to be made, the lid is removed from this box and the absorbing medium 

 is adjusted at a definite distance from the skin. About 1725 calories 

 are lost by the skin which corresponds to a loss of 69 per cent, of the 

 total, provided the latter is estimated at 2500 calories for each 24 

 hours. The quantity of water evaporated from the skin may be esti- 

 mated at 660 grm. in 24 hours. Since 0.582 calorie are needed to con- 

 vert each gram of water into vapor, about 381 large calories are lost in 

 this way. This corresponds to a loss of 15.3 per cent., making a total 

 for the skin of about 85 per cent, of the entire heat dissipation. 



The quantity of water evaporated from the pulmonary passage, 

 is estimated at 400 grm. As each gram requires 0.582 calorie to con- 

 vert it into vapor, the total loss effected through this channel amounts 

 to about 232 calories, or 9.4 per cent, of the total. An additional 

 3.8 per cent, is apportioned to the inspiratory air to warm it to the 

 temperature of the body. The remaining loss is covered by the warm- 

 ing of the food and drink upon its entrance into the body, and by the 

 loss suffered upon its subsequent discharge from the body in the form 

 of feces and urine. Estimated at 3 kilos with an initial average tem- 

 perature of 12° C, about 60 calories are dissipated in this way. This 

 indicates a loss of 2.8 per cent, of the total. 



The many factors which may vary the intensity of heat-dissipation 

 may conveniently be classified as involuntary and voluntary. Among 

 the former are to be mentioned those reflexes which give rise to vaso- 

 motor, pilomotor and secretomotor reactions. It is a matter of 

 every day experience that the skin and subcutaneous tissues pale under 

 the influence of cold and flush under the influence of warmth. These 

 changes indicate that cold constricts the cutaneous blood-vessels and 

 drives the blood into the deeper parts of the body in an endeavor to 

 diminish heat-dissipation. Warmth, on the other hand, relaxes these 

 vessels and allows a more rapid escape of the body-heat. In the first 

 case, thermolysis is also hindered in a varying measure by the secretion 

 of the sebaceous glands, which the northern people carefully preserve 

 and augment by anointing their body with oil and lard. Quite 

 similarly, the aquatic animals are in possession of special glands which 

 serve the purpose of covering their body with a fatty secretion. The 

 function of the latter is to diminish friction and to protect them more 

 thoroughly against an undue loss of heat. Upon this basis rests the 

 practice of swimmers to anoint their skin with fatty substances. In 

 the second case, the dissipation of heat may be greatly facilitated by 

 moistening the body-surface with the secretion of the sweat-glands. 

 In this way, a large part of the heat is lost in the form of latent or 

 bound heat, and naturally, the higher the outside temperature and the 

 dryer the air, the more rapid must be the evaporation and loss of heat. 

 Contrariwise, a warm but humid atmosphere prevents the evaporation 

 of the sweat and dissipation of heat. It is this secretomotor mechan- 



