206 PHILOSOPHICAL TRANSACTIONS. [aNNO 1792. 



survived an equally long exposure to the higher degrees of cold of the atmosphere, 

 in the same circumstances, does not appear. Though in the case related, im- 

 mersion in water did not prevent thirst, yet there is no doubt that it alleviated it, 

 a circumstance of high importance towards the preservation of life. 



p. s. I have purposely avoided any reasoning on the causes of the loss of \atal 

 heat on the change of media in the experiments recited. It may be supposed that 

 during immersion, the water immediately in contact with the skin having become 

 heated to a certain degree, the naked body, on rising from it into the air, was in 

 fact exposed to a colder medium, and thus the loss of heat, in this instance, pro- 

 duced. My examination of the heat of the water during immersion not having 

 been made in contact with the body, I will not deny that there is some founda- 

 tion for the remark ; and the cases, it must be allowed, are by no means exactly 

 parallel between immersion in an open vessel, however large, and immersion 

 in the sea, where the constant undulation may be presumed to occasion a 

 continual change in the surrounding fluid. But whatever allowance may 

 be made for the circumstance mentioned, I am persuaded that, the differ- 

 ence between the density of air and water being considered, it is not sufficient 

 to explain the loss of heat in the instance alluded to. The changes of tempe- 

 rature in the living body are governed by laws peculiar to itself. I have 

 found, in certain diseases, greater and more sudden variations than any men- 

 tioned, from applications of cold very gentle in degree, and momentary in 

 duration. 



In his masterly " Experiments and Observations on Animals producing Heat," 

 Mr. Hunter has objected to taking the heat of the human body by introducing 

 the bulb of the thermometer into the mouth, because it may be affected by the 

 cold air in breathing. The objection is well founded if the bulb be placed on the 

 upper surface of the tongue, but if it be under it and the lips shut, the effects of 

 respiration may be disregarded, as I have found from many hundred expts. The 

 heat may be observed in this way with ease and certainty, by employing thermo- 

 meters curved at that end to which the bulb is affixed (the bulb being introduced 

 at the corner of the mouth), some of which have been made for me by Mr. 

 Ramsden according to a form given, as well as others on Mr. Hunter's plan. 

 From repeated trials it appears to me, that when the usual clothing is on, the 

 heat of the living body may be taken, with nearly the same result and equal 

 certainty, under the tongue with the lips shut, at the axilla with the arm close to 

 the side, and in the hollow between the scrotum and the thigh ; every other part 

 of the surface is liable to variation and uncertainty. It is evident that of these 3 

 methods, the first only can be employed, as far as I can discover, when the trunk 

 of the body is immersed in water ; and even when the naked body is exposed to 

 the cold air, the first method seems the best, the heat remaining most steady 



