380 PHILOSOPHY OF ZOOLOGY. 



whether the air is moist or dry. And in the case of frogs 

 and dogs, Dr CRAWFORD found that the cold was generat- 

 ed even when the body was immersed in water. 



Even when the heating cause is applied only to a par- 

 ticular part of the body, as (in the experiments of Dr 

 HUNTER) to the urethra, its temperature is not increas- 

 ed beyond that degree to which the whole body may be 

 raised. 



In all these experiments in which the body is exposed 

 to a high temperature, the generation of cold is effected by 

 a great expenditure of the vital energy. Hence a great 

 degree of weakness is produced by continuing the effort. 



As the power of the whole body for the production of 

 cold appears to be limited, so is likewise the power of par- 

 ticular parts, " which (says BLAGDEX *) may be one rea. 

 son why we can bear for a certain time, and much longer 

 than can be necessary to fully heat the cuticle, a degree of 

 heat which will at length prove intolerable." It is proba- 

 ble that this power of the human body is greatly influen- 

 ced by habit, in the case of washer-women, whose hands 

 are frequently immersed in warm water, and glass-blowers, 

 whose bodies are exposed to a degree of heat, which to 

 others would prove painful. 



3. When the body is exposed to a temperature greatly 

 lower than the ordinary standard, a counteracting influ- 

 ence is exerted, and Jieat is generated. In the experiments 

 already quoted it appears evident, that there is an inferior 

 as well as a superior limit to the change of temperature in 

 living bodies, from the influence of surrounding objects. 

 In the experiments of Dr CUBRIE, the heat of the human 



Phil. Trans. 1775, p. 121. 



