330 REGULATION OF THE TEMPERATURE. 



owing to the stimulation of their metabolism, while the excretion of urea is also increased in 

 animals and in man ( 133, 5). 



(3) Cold acting upon the skin causes involuntary muscular movements 

 (shivering, rigors), and also voluntary movements, both of which produce heat. 



The cold excites the action of the muscles, which is connected with processes of oxidation 

 [PMUger). After poisoning with curara, which paralyses voluntary motion, this regulation of 

 the heat falls to a minimum [BShrig and Zuntz), [while the bodily temperature rises and falls 

 with a rise or fall in the temperature of the surrounding medium]. 



(4) Variations in the temperature of the surroundings affect the appetite 

 for food : in winter, and in cold regions, the sensation of hunger and the appetite 

 for the fats, or such substances as yield much heat when they are oxidised, are 

 increased ; in summer, and in hot climates, they are diminished. Thus the mean 

 temperature of the surroundings, to a certain extent, determines the amount of the 

 heat-producing substances to be taken in the food. 



II. Regulatory Mechanisms governing the Excretion of Heat or Thermolysis. 

 The mean amount of heat given off by the human skin in twenty-four hours, by 

 a man weighing 82 kilos., is 2092 to 2592 calories, i.e., 1*36 to 1*60 per minute. 



(1) Heat causes dilatation of the cutaneous vessels; the skin becomes red, 

 congested, and soft ; it contains more fluids, and becomes a better conductor of 

 heat ; the epithelium is moistened, and sweat appears upon the surface. Thus 

 increased excretion of heat is provided for, while the evaporation of the sweat also 

 abstracts heat. 



The amount of heat necessary to convert into vapour 1 grm. of water at 100 C, is equal to 

 that required to heat 10 guns, from 0to 53*67 C. The sweat as secreted is at the temperature 

 of the body ; if it were completely changed into vapour, it would require the heat necessary to 

 raise it to the boiling point, and also that necessary to convert it into vapour. 



Cold causes contraction of the cutaneous vessels ; the skin becomes pale, less 

 soft, poorer in juices, and collapsed ; the epithelium becomes dry, and does not 

 permit fluids to pass through it to be evaporated, so that the excretion of heat is 

 diminished. The excretion of heat from the periphery, and the transverse thermal 

 conduction through the skin, are diminished by the contraction of the vessels and 

 muscles of the skin, and by the expulsion of the well-conducting blood from the 

 cutaneous and subcutaneous vessels. The cooling of the body is very much affected, 

 owing to the diminution of the cutaneous blood-stream, just as occurs when the 

 current through a coil or worm of a distillation apparatus is greatly diminished. 

 If the blood-vessels dilate, the temperature of the surface of the body rises, the 

 difference of temperature between it and the surrounding cooler medium is increased, 

 and thus the excretion of heat is increased. Tomsa has shown that the fibres of 

 the skin are so arranged anatomically, that the tension of the fibres produced by 

 the erector pili muscles causes a diminution in the thickness of the skin, this result 

 being brought about at the expense of the easily expelled blood. 



By the systematic application of stimuli, e.g., cold baths, and washing with cold water, the 

 muscles of the skin and its blood-vessels may be caused to contract, and become so vigorous and 

 excitable, that when cold is suddenly applied to the body, or to a part of it, the excretion of 

 heat is energetically prevented, so that cold baths and washing with cold water are, to a certain 

 extent, "gymnastics of the cutaneous muscles," which, under the above circumstances, protect 

 the body from cold. 



(2) Increased temperature causes increased heart-beats, while diminished 

 temperature diminishes the number of contractions of the heart ( 58, II., a). 

 The relatively warm blood is pumped by the action of the heart from the internal 

 organs of the body to the surface of the skin, where it readily gives off heat. The 

 more frequently the same volume of blood passes through the skin twenty-seven 

 heart-beats being necessary for the complete circuit of the blood the greater will 

 be the amount of heat given off, and conversely. Hence, the frequency of the 

 heart-beat is in direct relation to the rapidity of cooling. In very hot air (over 



