13 



the experiments of this investigator showed conclusively that the normal 

 path for the message from mucous membrane of mouth to gland lay 

 through the central nervous S5 7 stem. The nerves involved in the reflex 

 secretion of saliva were determined, as well as their central connections. 

 In such a case as this, where all kinds of material dry, fluid, pleasant, 

 or harmful may be taken into the mouth, a rapid response of the salivary 

 glands is necessary to provide for the speedy swallowing of the food or to 

 facilitate its expulsion from the mouth. When the food has once under- 

 gone a preliminary warming and moistening in the mouth, and has been 

 passed, so to speak, by the critical organs of taste and smell placed at 

 the commencement of the alimentary tract, a rapid reaction of the other 

 glands of the alimentary canal i.e., one occupying fractions of a second 

 would not seem to be absolutely necessary. The predominant part, how- 

 ever, played by the central nervous system in all the most direct reactive 

 phenomena of the body led physiologists to search for similar reflex 

 nervous mechanisms of secretion through the rest of the alimentary 

 canal, and the firm faith that such nervous mechanisms existed was in no 

 way damped by the difficulties experienced in the attempts to determine 

 their existence and their paths. Thus for many years the only known 

 method of exciting gastric secretion was the introduction of irritant sub- 

 tances into the stomach, apart, that is to say, from the taking of a meal 

 which would excite in physiological fashion a secretion of gastric juice. 

 In the case of the pancreas Heidenhain observed on a few occasions a 

 scanty secretion from stimulation of the medulla oblongata, but could not 

 obtain this result at will. Succus entericus was obtained by some 

 observers from intestinal fistulae by mechanical stimulation of the mucous 

 membrane, and the so-called paralytic secretion of succus entericus was 

 produced in certain circumstances in a denervated loop of intestine. 



These were the sole indications of any influence of the nervous 

 system on the secretions below the mouth until the subject was taken up 

 by Pawlow at St. Petersburg. This observer realised that the last word 

 could not be said on any physiological question until experiments had 

 been made on an animal in an absolutely physiological condition, i.e., 

 with normal blood pressure, free from fear or pain, and unpoisoned by 

 anaesthetics. To effect this aim Pawlow has enriched physiology with 

 a new technique. By the exercise of scrupulous asepis, and aided by his 

 great surgical skill, he has succeeded in making observations on the 

 digestive process in animals by providing them with fistulous openings 

 into different parts of the alimentary canal, or with culs-de-sac which were 

 in nervous and vascular continuity with the rest of the canal, and whose 

 activity could be taken as samples of the activity of the whole organ from 

 which they were cut off. The results obtained by this physiologist seem 

 at first to point to an extension throughout the alimentary canal of pro- 

 cesses similar to those occurring in the mouth, and to prove that every 

 gland in the canal is excited reflexly through the central nervous system 

 by the presence of the foodstuffs in different stages of digestion at the 

 appropriate part of the lumen of the canal, 



