ii THE THERMIC ECONOMY OF THE ORGANISM 79 



contraction of the muscles on this side, seems to me to confirm 

 this phenomenon. Pflliger considers that the sense of tension and 

 rigidity in muscles exposed to external cold is in proportion to the 

 exaggeration of the reflex tone which is associated with increased 

 intensity of chemical change in the muscles. When the sensation 

 of cold increases owing to the skin becoming colder, shivering in 

 the form of trembling and spasms in the muscles begins by reflex 

 action, and greatly increases the respiratory processes and the 

 production of heat, and thus prevents the internal temperature of 

 the body from falling below the normal. We have a good example 

 of this in the effects of a cold shower-bath, which does not lower 

 the internal temperature, but, on the contrary, quickly raises it 

 one- or two-tenths of a degree. This is obviously the result of 

 the shivering, i.e. of the convulsive muscular contractions, which, 

 caused reflexly by the shower-bath, bring about a violent increase 

 in the production of heat. 



In addition to shivering caused by reflex action, Richet distin- 

 guishes shivering of central origin, due to the action of exogenous 

 or endogenous poisons. One classical example will be sufficient. 

 Injections of chloral or chloralose acting upon the nerve-centres 

 cause narcosis in dogs, during which the temperature of the 

 animal falls to 32-30. When the effects of the intoxication 

 pass off and the animal awakes, its temperature gradually rises 

 as the result of the shivering accompanying its awakening. 

 Richet found that during the narcosis, when there is no shivering, 

 the animal discharged a much smaller quantity of carbon dioxide 

 than during the shivering fit which accompanied the awakening. 

 This is a direct proof that the shivering intensifies the chemical 

 processes taking place in the muscles. 



The means which serve to maintain the average temperature 

 at an almost constant level involve in the case of protection from 

 cold&n increase in the production of heat; those which are intended 

 for protection against heat increase the loss of heat. This is clear 

 if we consider the fact emphasised by the researches of Voit, Page, 

 and Fredericq, that when the temperature of the environment 

 rises above 20-25 the processes of combustion in the organism 

 do not decrease, as they should do in order to prevent the tempera- 

 ture rising above the normal, but increase, as is proved by the 

 greater discharge of carbon dioxide ; the organism can only 

 protect itself against the heat by increasing the loss of heat either 

 by acceleration of the cutaneous circulation, the secretion of sweat, 

 or more rapid breathing. 



The immediate effect of an excessive rise in the external tem- 

 perature is a general dilatation of the cutaneous vessels ; a larger 

 quantity of blood circulates in the periphery of the body, where it 

 becomes cooler, because the external temperature in the large 

 majority of cases is lower than that of the circulating blood. 



