350 NOTES OF A NATURALIST. 



authorities, is that the phenomena here discussed are 

 of a very complex nature ; that different physical 

 agencies are concerned in the various effects produced 

 on the body ; and that most probably there are many 

 different pathological affections which have been 

 classed together, but which, when more fully studied, 

 will be recognized as distinct. 



In the first place, I apprehend that the action of 

 the sun which causes discolouration and blistering of 

 the skin has no relation to that which causes sun- 

 stroke. It is a local effect confined to the surfaces 

 actually exposed, and, if it could be accurately 

 registered, would serve the purpose of an actinometer, 

 depending as it does on the amount of radiant heat 

 reaching the surface in a unit of time. 



Sun-stroke proper is, I believe, an affection of the 

 cerebro-spinal system arising from the overheating of 

 those parts of the body. It is by no means confined 

 to the tropics, or to very hot countries, as many cases 

 occur annually in Europe, and still more frequently in 

 the eastern states of North America. 



Nearly allied to sun-stroke, but perhaps sufficiently 

 different to deserve separate classification, are those 

 attacks which some writers style cases of thermic 

 fever, which arise mainly in places where the body is 

 for a continuance exposed to temperatures exceeding 

 the normal amount of the human body. In producing 

 thermic fever, it would appear that the depressing 

 effect of a hot moist climate acts powerfully as a 

 predisposing cause, and such cases not uncommonly 

 arise where there has been no exposure whatever to 

 the direct rays of the sun. 



