854 REGULATION OF PRODUCTION OF HEAT. [BOOK n. 



tractions. At the same time the heat given out by the muscles 

 will be temporarily increased at every contraction which may occur. 

 Thus, the shivering which follows exposure to cold distinctly helps 

 to warm the body; indeed some observers have been led to think 

 that, in man, this visible effect of cold plays a more important 

 part in his heat regulation than the invisible actions which we 

 have just described. We may also add that the regulative nervous 

 mechanism may apparently be overborne by an exposure to too 

 great heat or cold. When for instance the cold to which the 

 animal is exposed becomes excessive, the reaction of the thermo- 

 taxic nervous system is powerless against the direct action on 

 the tissues of the depressing influences, and the metabolism, 

 together with the temperature, sinks. 



The results with urari just mentioned seem to shew that 

 this thermotaxic nervous mechanism bears chiefly on the skeletal 

 muscles. Whether the glandular organs take any part in it, or 

 whether they have a metabolic thermotaxic machinery of their own, 

 of such a kind for example that the increase of heat production 

 due to food is the result not so much of the immediate consumption 

 of part of the food itself (luxus consumption) as of the presence of 

 food, in the alimentary canal or after absorption, stirring up the 

 liver to increased metabolism, we do not at present know. 



535. In a number of experiments it has been shewn that 

 injuries to, such as those caused by puncture or galvanic cautery, 

 or electrical stimulation of limited portions of the more central 

 portions of the brain may give rise to a great increase of the 

 temperature of the body without producing any other marked 

 symptom. The increase is shewn, by the increase of metabolism, 

 increased production of carbonic acid, increased consumption of 

 oxygen, and, we may add, increased excretion of nitrogen, as well 

 as by direct calorimetric observations, to be due to an increased 

 production of heat. This naturally suggests that the portions 

 of the brain in question contain the hypothetical heat centre just 

 mentioned, the lesion on stimulation exciting the centre to activity 

 by direct action on it, instead of in the usual reflex manner. The 

 matter has not however as yet been clearly worked out ; and 

 indeed observers are not agreed as to the exact parts of the brain 

 injury to which, or stimulation of which, produces the effect. 

 While some place it in the median and basal portions of the 

 corpus striatum, others maintain that it is situated in the optic 

 thalamus. The fact however remains that an affection of a very 

 limited portion of the central nervous system may, without pro- 

 ducing any other obvious effects, so increase the heat production 

 of the body as to raise the temperature of the body several 

 degrees. 



536. By regulative mechanisms of the kind just discussed 

 the temperature of the warm-blooded animal is maintained within 

 very narrow limits. In ordinary health the temperature of man 



