INTERNAL WORK. 373 
CausE OF THE INCREASE.—Two possible explanations of the 
above fact naturally suggest themselves, viz., that, on the one hand, 
the more abundant supply of food material to the cells of the 
body may act as a direct stimulus to the metabolic processes, or, 
on the other hand, that the increased metabolism may arise from 
the greater activity of the organs of digestion, or finally, that both 
causes may act simultaneously. 
The results obtained by Speck,* who found that the increase 
began very promptly (within thirty minutes) after a meal, would 
indicate that it can hardly be due to a stimulating action of the _ 
resorbed food upon the general metabolism, but must arise, in 
large part at least, from the activity of the digestive organs. 
Specific investigations upon this point were undertaken by Zuntz & 
v. Mehring.t They found that glycerin, sugar, egg-albumin, puri- 
fied peptones, and the sodium salts of lactic and butyric acids { 
when injected into the circulation caused no material increase in 
the amount of oxygen consumed as determined in successive short 
periods by the Zuntz form of respiration apparatus. It is well estab- 
lished that some of these substances do increase the metabolism 
when given by the mouth, and the authors verified this fact for sugar 
and for sodium lactate and likewise showed that substances like 
sodium sulphate, which are not metabolized in the body, caused a 
similar rise in the metabolism when introduced into the digestive 
tract. They therefore conclude that the effect of the ingestion of 
food upon the metabolism is due chiefly to the expenditure of energy 
required in its digestion. Wolfers § and Potthast,|| in experiments sup- 
plementary to those just mentioned, obtained confirmatory results. 
On the other hand, Laulanié,{ in the experiments mentioned 
on p. 180 in their bearings upon the formation of fat from carbo- 
hydrates, obtained almost as marked an increase in the oxygen 
consumption subsequent to the injection of sugar into the circula- 
tion as after its administration by the mouth. 
* Arch, exper. Pathol. and Pharm.., I, 1874, p. 405. 
+ Arch. ges. Physiol., 15, 634; 82, 173. 
} The results of their experiments upon organic acids have already been 
cited in Chapter V, p. 157, in another connection. 
§ Arch. ges. Physiol., 32, 222. 
\| Ibid., 32, 280. 
{ Archives de Physiol., 1896, p. 791. 
