ANIMAL HEAT 587 



paralyzed by curara. This, even if true, would not support the 

 conclusion that a ' nervous fever ' that is to say, a fever due 

 solely to increased metabolism in the nervous system exists ; 

 for in a curarized animal a large amount of ' active ' tissue 

 (glands, heart, smooth muscle) still remains in physiological 

 connection with the brain and cord. But, as a matter of fact, 

 in an animal under a dose of curara sufficient to completely 

 paralyze the skeletal muscle cocaine causes no appreciable rise 

 of rectal temperature ; and this is strongly in favour of the view 

 that the fever produced in the non-curarized animal is con- 

 nected with excessive muscular metabolism. 



Regulation of Temperature or Thermotaxis. What, now, is 

 the mechanism by which the balance is maintained in the homoio- 

 thermal animal between heat-production and heat-loss ? In 

 answering this question we have to recognise that both of these 

 quantities are variable, that a fall in the production of heat may 

 be compensated by a diminution of heat-loss, and an increase 

 in the loss of heat balanced by a greater heat-production. 



The loss of heat from the surfaces of the body may be regu- 

 lated both by involuntary and by voluntary means. It is greatly 

 affected by the state of the cutaneous vessels, and these vessels 

 are under the influence of nerves. A cold skin is pale, and its 

 vessels are contracted. In a warm atmosphere the skin is 

 flushed with blood, its vessels are dilated, its temperature is 

 increased ; an effort, so to speak, is being made by the organism 

 to maintain the difference of temperature between its surface 

 and its surroundings on which the rate of heat-loss by radiation 

 and conduction depends. A still more important factor in man, 

 and in animals like the horse, which sweat over their whole 

 surface, is the increase and decrease in the quantity of water 

 evaporated and of heat rendered latent. It is owing to the 

 wonderful elasticity of the sweat-secreting mechanism, and to 

 the increase of respiratory activity and the consequent increase 

 in the amount of watery vapour given off by the lungs, that men 

 are able to endure for days an atmosphere hotter than the 

 blood, and even for a short time a temperature above that of 

 boiling water. The temperature of a Turkish bath may be as 

 high as 65 to 80 C. Blagden and Fordyce exposed themselves 

 for a few minutes to a temperature of nearly 127 C. Although 

 meat was being cooked in the same chamber by the heat of the 

 air, they experienced no ill effects, nor was their body-temperature 

 even increased. But a far lower temperature than this, if long 

 continued, is dangerous to life. During the ' hot waves, ' not infre- 

 quently experienced in summer in the United States, hundreds 

 of persons have died within a few days from the excessive heat. 

 It is stated that during the unusually hot summer of 1819 the 



