INFLUENCE OF NERVOUS SYSTEM. 539 
sequence of psychical conditions, o.-sophageal fistula' were made, and the 
saliva was prevented from passing into the stomach. 
In RichetV observations on a human subject, who, by swallowing a 
caustic alkali, had rendered the oesophagus impassable, and in whom con- 
sequently it had become necessary to make an opening into the stomach, 
it was observed that chewing Bavoury food, none of which passed into 
the stomach, produced a copious flow of gastric juice. It was not 
possible in thesi to absolutely assert that this resulted from 
nervous influence acting directly on the secreting epithelium, for move- 
ments of the stomach may have brought about the flow, but the quan- 
tity secreted suggested a direct nervous influence. That there is such 
a direct nervous influence has been conclusively proved by Pawlow, 2 
in conjunction with Schoumow-Simanowsky. Their experiments were 
made on dogs which had had a portion of the stomach isolated in the 
manner already described, care being taken that the nervous connections 
were intact. In addition, the cesophagus was separated, the cut ends 
being attached to openings in the neck, so that swallowed food passed 
out at one opening, and, through the other, food which it was desired 
should enter the stomach could be passed in. It was possible, therefore, 
to bring the animal under the influence of food in three ways. In the 
first place, it might he shown f< «od, but the food would not be actually 
introduced into the stomach. This constituted the so-called -psychical 
feeding." 3 Secondly, the animal might he fed by the mouth, but none 
of the food allowed to enter the stomach, since it would make its exit 
at the oesophageal opening. This was described as "pseudo-feeding*' 
(Scheinfiitterung). Thirdly, by the introduction of food into the lower- 
division of the oesophagus, true feeding was carried on. The results 
varied according to the method adopted. The latent period, or period 
elapsing after administration before secretion commences, is in the dog 
about seven minutes. This does not vary much whether it be a case of 
psychical, pseudo-, or true feeding. The latter course of secretion shows. 
however, considerable variations. This was the first poinl established 
by Pawlow. 
He next attempted to discover the paths of the nervous impulses 
bringing about these changes. Section of the splanchnics did not 
affect the results, but after severing both vagi the reflex secretion 
was absent. With one vagus cut (the right), the animal was found to 
respond in the usual way. Later the left vagus was divided without 
anaesthesia. The animals live for a few days in this condition, but 
during this time no reflex secretion occurs. From this it was concluded 
that the impulses constituting the efferent portion of the reflex act pass 
along the vagi. But more positive results in this connection were 
obtained by Pawlow by stimulating the peripheral ends of the cut vagi. 
If, some twenty-four hours after the second section, the cut end lie stimu- 
lated, — and it is better to do this by applying induction shocks at the 
rate of one per second, rather than by using the rapidly interrupted 
1 " Le sue gastrique chez l'homme et les animaux," Paris, 1878. 
2 " Die Innervation der Magendriisen beim Hunde," Arch. f. Physiol., Leipzig, 1895. 
3 Though the exhibition of food to the dog, which had been operated on in the manner 
described above, evoked a flow of gastric juice, if, from previous experience, the dog was led 
to understand that the food would not actually be given, the secretion very soon stopped. 
It may be mentioned that Heidenhain did not regularly obtain a flow as the result of 
showing the animal food, and this suggests that his method involved interference with the 
nervous tracts. 
