DIGESTION OF FOOD. 828 
known to have a double nervous supply from the cerebro- 
spinal and the sympathetic systems. 
It would appear that, as the vaso-motor changes run paral- 
lel with the secretory ones, the vaso-motor and the proper 
secretory centers act in concert, as we have seen holds of the 
former and the respiratory center. But it is to our own mind 
very doubtful whether the doctrine of so sharp a demarkation 
of independent centers, prominently recognized in the physi- 
ology of the day, will be that ultimately accepted. 
Secretion by the Stomach.—The mucous membrane of St. Mar- 
tin’s stomach was observed to be pale in the intervals of diges- 
tion, but flushed when secreting, which resembled sweating, so 
far as the flow of the fluid is concerned. When the man was 
irritated, the gastric membrane became pale, and secretion was 
lessened or arrested, and it is a common experience that emo- 
tions may help, hinder, or even render aberrant the digestive 
processes, 
While the evidence is thus clear that gastric secretion is 
regulated by the nervous system, the way in which this is 
accomplished is very obscure. We know little of either the 
centers or nerves concerned, and what we do know helps but 
doubtfully to an understanding of the matter, if, indeed, it 
does not actually confuse and puzzle. 
Digestion can proceed in a fashion after section of the nerves 
going to the stomach, though this has little force as an argu- 
ment against nerve influence. We may conclude the subject 
by stating that, while the influence of the nervous system over 
gastric secretion is undoubted as a fact, the method is not 
understood; and the same remark applies to the secreting 
activity of the liver and pancreas. 
The Secretion of Bile and Pancreatic Juice— When the contents 
of the stomach have reached the orifice of the discharging bile- 
duct, a large flow of the biliary secretion takes place, probably 
as the result of the emptying of the gall-bladder by the con- 
traction of its walls and those of its ducts. This is probably 
a reflex act, and the augmented flow of bile when digestion is 
proceeding is also to be traced chiefly to nervous influences 
reaching the gland, though by what nerves or under the gov- 
ernment of what part of the nervous centers is unknown. 
Very similar statements apply to the secretion of the pancre- 
atic glands, though this is not constant, as in the case of bile— 
at all events, in most animals. 
It is known that after food has been taken there is a sudden 
