SUBMAXILLARY GLAND. 381 



gland tends to replace its loss of proteid to a considerable 

 degree during activity. 



An explanation of the apparent discrepancy between the 

 figures for the total solids and those for the nitrogen in the 

 resting and active glands, seems to the writer to be found in 

 the columns giving the percentage of nitrogen in the solids. 

 In every experiment the solids from the active gland were 

 relatively richer in nitrogen than those from the resting. 

 This difference seems to justify the assumption that the active 

 glands had become poorer in carbon, hydrogen, and perhaps 

 oxygen. It suggests, also, that within the secreting cells 

 there was a vigorous combustion of carbonaceous material, 

 carbohydrate, fat, the carbon moiety of proteid, or some such 

 " explosive " combination of oxygen with substances rich hi 

 carbon as is held to be the source of heat and work in muscle. 

 Indeed, our knowledge of secretion points to such a combus- 

 tion as the source of the energy liberated within the gland. 

 Although recent investigations * have not verified Ludwig's f 

 observation that the saliva is warmer than the blood, it is 

 generally held to be very probable that a liberation of heat 

 occurs during secretion. The saliva contains a much larger 

 amount of carbonic acid than does the blood.J Physico- 

 chemical considerations prove that the separation of a fluid 

 like saliva, containing 0.4-0.6 per cent of salts, from a fluid 

 like the serum of the blood, containing 0.7-0.8 per cent of 

 inorganic matter, involves work. Ludwig showed that saliva 

 is secreted at a pressure higher than that of the blood in the 

 carotid; and O. F. F. Grimbaum has recently published 

 observations on the two kinds of work performed by the 

 secreting glands. The microscopical changes observed in the 

 secreting cells do not seem to offer any contradiction to 

 the view that a combustion occurs. Observations of Heiden- 

 hain || tend to show, also, that stimulation of the cervical 



* Bayliss and Hill, Journal of Physiology, 1894, xvi, p. 351. 

 t Ludwig, Wiener medicinische Wochenschrift, 1860, pp. 433, 449. 

 $ Pfliiger, Archiv f. d. ges. Physiol., 1868, i, p. 686. 

 Griinbaum, O. F. F., Journal of Physiology, 1898, xxii, p. 385. 

 || Heidenhain, Studien des physiologischen Institute zu Breslau, 1868, iv, 

 p. 66. 



