18 The Philippine Journal of Science wit 



ence that the acclimatization observed in the case of the monkey 

 consisted in the development of increased capacity for sweating 

 under the conditions of the experiment. 



Mechanism of this acclimatization. — It remains to inquire how 

 this increased sweating observed in acclimatized monkeys was 

 brought about. It followed upon simple exposure to the sun, 

 which means exposure to heat and light rays. The increase in 

 sweating occurred upon the surfaces most exposed to the heat, 

 namely, the palms of the hands, which came in contact with 

 the hot roof, and the back, which was uniformly turned toward 

 the sun. The primary effects of the heat upon the monkey were, 

 first, the elevation of the temperature of that portion of the skin 

 which was exposed to the heat rays, including, among other 

 structures there found, the sensory nerve endings, the secretory 

 cells, and the secretomotor nerve endings in the sweat glands; 

 secondly, the elevation of the temperature of the entire body, 

 most marked in the first few days of exposure. A secondary 

 effect evidently was an increase in sensitiveness of one or more 

 parts of the sweating mechanism, which increase was more or 

 less persistant. Since a small dose of atropin stops the sweating 

 in an acclimatized monkey, presumably by paralyzing the secre- 

 tomotor nerve endings in the sweat glands, the increase in sensi- 

 tiveness must lie in the nervous mechanism and not in the 

 secretory cells of the sweat glands. The three portions of this 

 nervous mechanism which seem most likely to be affected are 

 the sensory heat nerve endings, the secretomotor nerve endings 

 in the sweat glands, and the nerve cells concerned with temper- 

 ature regulation. The endings mentioned would be most affected 

 by the direct heating of the skin. The cells could be affected 

 in two ways: First, by the arrival of a greater number and 

 of stronger impulses, coming from the highly heated skin, and 

 secondly, by being heated above their normal temperature by 

 the increase in body temperature. Since, when stronger and 

 more frequent impulses pass into a given tract of the brain, the 

 brain becomes so changed that stimuli to this tract set up greater 

 responses than before, it does not seem unreasonable to suppose 

 that the nervous mechanism regulating body temperature, ex- 

 cited by the unusually strong heating of the skin, may become 

 so changed that any nerve impulses coming to it will produce 

 greater discharges than before. It may then be justifiable to 

 assume that the acclimatization observed in these experiments 

 consisted, at least in part, in a sensitization of nerve cells 

 concerned with temperature regulation of which cells those con- 



