896 METABOLISM. 



and the greater the amount of muscular activity the greater the amount 

 of oxidised materials in the form of carbonic acid and water that are 

 formed and got rid of from the body. It is probable that the oxidation 

 processes which occur in gland cells are by no means so active, for 

 although a gland when stimulated to activity receives a larger amount 

 of oxygenated blood, yet a considerable amount of the oxygen of that 

 blood simply passes through the capillaries without being absorbed, so 

 much so, in fact, that, as noted by Bernard, the blood of the veins of the 

 salivary glands during stimulation of their cranial nerves flows almost 

 as bright red as that of an artery. And in confirmation of this we find 

 that the largest gland in the body, the liver, is supplied with a relatively 

 small amount of arterial blood, and that almost the whole of its 

 metabolic activity is carried on with "blood which already has passed 

 through the intestinal capillaries, and which has thereby been deprived 

 of a large part of its oxygen. Further, it was noted by Ludwig that the 

 saliva flowing from the duct of the submaxillary gland contains more 

 oxygen, than is dissolved in the plasma of the arterial blood, an 

 indication that the cells of the salivary glands cannot be greedy of 

 oxygen since they pass oxygen out along with the secretion rather than 

 retaining it for the formation of carbon dioxide and water. The 

 salivary glands, moreover, have been shown by the recent careful 

 observations of Bayliss and Hill l not to produce any appreciable amount 

 of heat ; and although it is stated that the blood flowing through the 

 liver is the warmest blood in the body, 2 and warmer than that flowing 

 through the muscles, it must be borne in mind that it is almost 

 impossible to measure exactly the normal temperature of the blood 

 flowing from the muscles, because the operation necessary for observing 

 the temperature of such blood would tend to expose it to loss of heat. 3 



In conformity with the conclusion that the muscles are the organs which 

 possess by .far the greatest amount of metabolic activity, it has been estimated 

 that the muscular tissues contain about one-fourth of the whole blood of the 

 body. The liver, which has important special functions to perform in 

 metabolism functions which are, however, probably in large measure inde- 

 pendent of oxidation contains another fourth of the blood, one-fourth is 

 employed in keeping full the larger arteries and veins, and all the rest of the 

 body put together has for its capillary supply only the remaining fourth. It 

 is clear, then, that in all observations and experiments upon the metabolism 

 of the body, the metabolism of the muscles must occupy a prominent place. 



NITROGENOUS METABOLISM IN THE TISSUES. 



Of the proteids of the body Voit distinguishes two kinds (1) Those 

 which form an integral part of the living substance or bioplasm, and (2) 

 those which occur in the tissue juice and in contact with the bioplasm, 

 but which are not to be regarded as forming an integral part of that 

 substance itself. To this latter kind he has given the name of " circu- 



1 Journ. PhysioL, Cambridge and London, 1894, vol. xvi. p. 351. Previously to this 

 work, it had been accepted, on the authority of Ludwig and others, that the secretion of 

 saliva is accompanied by a marked production of heat within the submaxillary gland. 



2 See p. 826. Waymouth Reid was unable to find any effect on the temperature of the 



le result of stimulating the splanchnic and vagi nerves ("Proc. Phys. 



liver as the 



1895, p. xxxi., in Journ. PhysioL, Cambridge and London, vol. xviii.). 



3 In his experiments upon the gaseous exchange in blood perfused through "surviving " 

 mammalian muscle, v. Frey found that the blood leaving the muscle was slightly warmer 

 than that entering it (Arch. f. PhysioL, Leipzig, 1885, p. 559). 



