Among the various functions ascribed to the glands of internal secretion, the regulation of metabolism ranks high. Not only is it a very important part of their activity, but it is also the function about which the greatest and most accurate knowledge has been accumulated. Of course, the general regulation of metabolism is not wholly controlled by the glands of internal secretion, for there are many other factors which exert influences which cannot now be ascribed to the activity of these glands. Examples are found in the effect of exercise, the specific dynamic action of foodstuffs, fasting, sleep, etc., and it therefore cannot be assumed that these endocrine glands absolutely control the rate of metabolism. But there can be no doubt that their general influence is great.
As far as our knowledge goes, this influence is largely exercised on the heat production as a whole rather than on individual components