THE PRODUCTION AND DISSIPATION OF HEAT 1105 



with sufficient fuel to carry on even the most moderate muscular 

 activity. 1 Beyond this ordinary heat-production, the amount of fuel 

 needed by a person is in agreement with the character of the exercise. 2 

 Farmers require on an average 3500 calories and six-day bicycle riders 

 10,000 calories per day. Boys, on the other hand, need only about 

 1500 calories, and babies 100 calories for each kilogram of body weight. 

 The Effect of Varnishing the Skin and Other Procedures. The 

 larger the surface of the body exposed to the cooler medium, the greater 

 must be the loss of heat.- Consequently, since a small animal presents 

 a proportionately larger surface to the surroundings in relation to its 

 mass than a large animal, its loss of heat must exceed that of the latter. 

 Obviously, this more considerable thermolysis must be accurately 

 balanced by a greater thermogenesis, and hence, the smaller animal 

 must possess a more intense metabolism. This is evinced by its more 

 rapid respiratory and cardiac rates. 



While warm-blooded animals may survive a brief exposure to an outside 

 temperature of from 100 to 132 C., owing to the profuse loss of latent heat then 

 ensuing, cold-blooded animals are usually killed at about 40 C., because their 

 musculature enters at this temperature the state of rigor caloris. Insects commonly 

 withstand a temperature of 64 C. Even the ordinary temperature of a beehive 

 varies between 30 and 40 C. which represents stagnated heat produced by the 

 bees themselves. Plants wither at a temperature of 52 C. If left to themselves, 

 warm-blooded animals usually do not survive when their body-temperature has 

 been reduced to 20 C., but if artificial respiration and warmth are applied to them, 

 they may recover from a temperature even lower than the one just given. 

 Cold-blooded animals are able to withstand 1 C. and may even be partially frozen. 3 



The hibernating animals show signs of depression when their temperature falls 

 below 28 C. At 18 C. they exhibit a decided drowsiness, at 6 C. semi-sleep and 

 at 1.6 C. deepsleep. 4 At this time, the heart beats only 8 to 10 times in a minute, 

 while the respiratory movements cease altogether. The very small amount of 

 oxygen which they now require is obtained by means of the volumetric changes 

 which the heart undergoes during its cycle. On systole this organ becomes smaller, 

 causing a slight amount of air to flow into the lungs, while on diastole, it becomes 

 larger and forces an equal amount of air outward. This constitutes the so-called 

 cardio-pneumatic phenomenon. When the hibernating animal awakes, its body- 

 temperature may rise as much as 20 C. in the course of two hours. 5 



A rise in temperature may also result directly after death. Obviously, this 

 effect must be produced by a continued heat-production and a diminished heat- 

 dissipation, establishing a balance in favor of the former process. Thus, it may 

 happen that the sudden cessation of the circulation prevents the escape of heat 

 from the still active tissues. A most favorable condition of this kind is created 

 when the body-temperature has been high beforehand, so that the interruption of 

 heat-dissipation may allow an excessive stagnation of heat in the highly active 

 tissues. Muscular spasms at the time of death augment this effect. Heat is also 

 produced during the fixation of the muscles coincident with the onset of rigor mortis. 



Covering the skin with a layer of varnish or paraffin has the same effect as cooling, 

 because an animal so treated loses heat very rapidly, owing to the dilated condition 



x Lusk, Science of Nutrition, W. B. Saunders and Co., 1909. 



2 Rumf, Pfluger's Archiv, xxxiii, 1884, 538, and Knoll, Archiv fur Exp. Path, 

 und Pharm, xxxvi, 1895, 305. 



3 Muller-Erzbach., Zoolog. Anz., 1891. 



4 Merzbacher, Ergebn. der Physiol., Hi, 1904, 14. 

 6 Pembrey, Jour, of Physiol., xxix, 1903, 195. 



70 



