816 REGULATION OF PRODUCTION OF HEAT. [BOOK n. 



the skin leads to a decrease, of the muscular metabolism. Further, 

 the centre of this thermotaxic reflex mechanism appears to be 

 placed somewhere in the nervous system above the spinal cord. 

 When urari is given, the reflex chain is broken at its muscular 

 end; when the spinal cord is divided the break is nearer the 

 centre. Whether we should conclude that the working of this 

 reflex mechanism is of such a kind that cold to the skin excites 

 the centre to a heat-producing activity, or of such a kind that 

 warmth to the skin inhibits a previously existing automatic 

 activity of the centre, may be left for the present undetermined. 



We may add that the muscular metabolism which thus helps 

 to regulate temperature need not involve visible muscular con- 

 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 and increased consumption of 

 oxygen, 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 



