54o MECHANISM OF SECRETION OF GASTRIC JUICE. 
current, — there results a flow of gastric juice. A certain interval occurs 
before the secretion is manifest, which is to be referred to changes 
actually taking place in the epithelium of the stomach. The character 
of the secretion varies according to the stage of the digestive act and the 
nature of the food. This will be again referred to in a later section. 
It must be mentioned that some observers have not had the same success 
in showing the secretory importance of the vag'us nerve. That certain differ- 
ences are perceptible in consequence of its excitation, they admit, but they 
refer the variations rather to the altered power of muscular contraction 
possessed by the stomach. Thus Leubuscher and Schafer : experimented 
both upon rabbits and dogs, performing the operations according to Pawlow's 
method. They frequently used a control animal for precision in estimating 
the change. As far as variations in the amount of hydrochloric acid were 
concerned, they came to the conclusion that there was no constant difference. 
The stomach they found invariably relaxed, and the food introduced within 
was, after a prolonged interval, found to be arranged in two zones, one against 
the walls of the stomach, which was well digested and contained hydrochloric 
acid in normal amount, that occupying the centre of the viscus being poor in 
acid and rapidly becoming decomposed. As far as stimulation of the peripheral 
stump of the vagus was concerned, they did not obtain constant results, but 
they appear to have adopted the rapidly interrupted current rather than the 
induction shocks at prolonged intervals used by Pawlow. That the food was 
not perfectly mixed, is obvious from their experiments. This will probably 
explain the decomposition occurring ; this change was noticed also by Pawlow to 
come on a few days after section of both vagi. It is, however, to be noted that 
they were unable to confirm the passage of secretory impulses along the vagus. 
There exists one observation upon the human being from which it seems 
that stimulation of the vagus may cause a flow of gastric juice. Regnard and 
Loye 2 stimulated the vagus in a decapitated criminal some forty-five minutes 
after death. Numerous drops of gastric juice appeared over the surface of the 
stomach. This may also, however, have been the result of movements of the 
stomach, which they observed at the same time to occur. 
The conditions under which local stimulation provokes secre- 
tion. — As already stated, it has been held by many that simple 
mechanical irritation of the mucous membrane will directly produce a 
How of gastric juice. Beaumont 3 showed that mechanical irritation of 
the mucous membrane caused increased vascularity and the appearance 
of small drops of gastric juice, and he further pointed out that the effect 
is confined to the irritated locality, and that the amount of juice secreted 
is small in quantity. Tiedemann and Gmelin, 4 Heidenhain, 5 and 
others also state that the secretion is limited. Pawlow states that 
the amount secreted is practically nothing, when indigestible substances 
such as pebbles are placed in the stomach. It may therefore be 
regarded as probably true that any secretion produced by simple 
mechanical irritation is extremely small, and the existence of this slight 
secretion in no way suggests that the normal secretion can be looked 
upon as the result, to any great extent, of such stimulation. On the 
other hand, stimulation by food, even if solid, is much more effectual. 
1 "Ueber die Beziehungen des Nervus Vagus zur Salzsiiure-seeretion des Magenschleim- 
haut," Ccntralbl. f. in acre Med., Leipzig, 1894, Bd. xv. 
2 "Recherches faites a Amiens sur les restes d'un supplicie," Compt. rend. Soe. de hiol.. 
Paris, 1887. 
3 Op. cit. 4 Op. rit. 3 Arch. f. d. yes. Physiol., Bonn, 1879, Bd. xiw 
6 Address at St. Petersburg. Reported in Brit. Med. Journ., London, 1895. 
