Why and wherefore is the secretion instituted by psychic influence maintained? What would first occur to all your minds is naturally the immediate influence which the food exerts upon the walls of the stomach. And this is true, but it does not happen in the simple, direct fashion current in the minds of many physiologists and physicians. When I said that bread or boiled white of egg, introduced directly into the stomach, may not for hours produce a trace of secretion, probably many of my hearers may have asked themselves with natural astonishment, "How, then, is the effect of the forced feeding of phthisical and insane patients, and the artificial feeding of those with gastric fistulae (performed on account of stricture of the oesophagus) to be explained?" I will introduce my answer by a very unexpected pronouncement relative to the assertion that mechanical stimulation of the stomach wall by food constitutes a reliable and effective means of calling forth the secretory work of the glands. This assertion, which is so categorically set forth in many text-books of physiology, and which consequently has gained hold of the mind of the physician, is nothing else than a sad misconception degenerated into a stubborn prejudice.

My own statement, repeated in many published articles, and at the meetings of various medical societies, that this dictum is only a picture of the imagination, has met, for the most part, either with an unbelieving shake of the head or else with a direct avowal that "it cannot be so." I regret exceedingly that these steadfast unbelievers are not here, so that we might together bring the matter before the tribunal of fact, to the demonstration of which we will now proceed. To this matter I attribute very great importance. It is on this ground, according to my opinion, that the whole battle must be fought out between the generally accepted view that every agency is capable of exciting the gastric mucous membrane and the theory that it is only excitable by specific and selected stimuli. If once the defenders of the old opinion are driven from their position and obliged to admit the inefficiency of mechanical stimulation, there would be nothing further left for them than to build up new theories and search out old facts concerning gland work which have hitherto been rigidly kept in the shade.

We may take it that it is mainly because people were so seized with the belief in the direct and simple mechanical explanation that Bidder and Schmidt's experiment of the excitation of gastric secretion by mental effect has been so little taken into consideration, notwithstanding that it appeared so thoroughly reliable and convincing.

I will now repeat the experiment of mechanical stimulation of the gastric mucous membrane before you in the well-known, traditional, and classic manner. Here is a dog with a gastric fistula on which a cervical cesophagotomy has in addition been performed. I open the fistula; as you see, nothing flows out of the stomach; it was washed out clean with water an hour ago. We take the celebrated feather and also a tolerably strong glass rod. Folds of blotting-paper saturated with red and blue tincture of litmus are placed at hand. I now ask my assistant to continuously move the feather and glass rod, alternately, in all possible directions in the stomach, changing from one to the other every five minutes. On removal from the stomach each is carefully dried with red and blue blotting-paper. You have all seen, gentlemen, that this procedure has now been kept up for half an hour. From the fistular orifice not even a single drop has escaped, and, moreover, the drops of moisture on all the pieces of red blotting-paper I have been able to hand to you have assumed a distinct blue tinge, caused by the moisture of the alkaline mucous membrane. The blue pieces, however, have merely been made wet without altering their colour.

Consequently, with the most thorough mechanical stimulation of the whole cavity of the stomach, we have not been able to find a single spot possessing a noticeable acid reaction. Where, then, are the streams of pure gastric juice of which we read in text-books! What objection can be raised against the conclusiveness of this experiment? In my opinion only one: that we are dealing with a dog out of health, whose gastric glands from some possible cause are unable to react normally. This single objection can be set aside before your eyes. After failing with the mechanical stimulation, we proceed forthwith to the sham feeding of the same animal. The dog takes the food offered it with keen appetite, and you see that, exactly five minutes after beginning the feeding, the first drops of juice appear from the stomach, followed by others faster and faster. I catch a couple of drops on the blue litmus paper, and you see that they produce bright red specks on the blue sheet. After thirty minutes' sham feeding we have collected 150 c.c. of juice, which, without filtering, looks as clear and transparent as water.

We cannot, therefore, possibly doubt that, when the proper stimulus is used, the gastric glands react to it in a perfectly normal fashion, furnishing a healthy gastric juice. From this it irrefutably follows that only one explanation is to be found for the negative result in the first half of our experiment, viz., that the mucous membrane of the stomach, so far as secretory activity goes, is perfectly indifferent to mechanical excitation. And yet this mechanical stimulus is demonstrated as an exciting agency in the physiological lecture theatre. I venture to think that this lecture experiment from now onwards will quit the field, and give place to the one I have just shown you. This apparently simple experiment of mechanical stimulation can, however, only be successfully performed when certain very obvious rules are followed. These, however, physiologists have not observed, probably on account of a preconceived belief in the effectiveness of the mechanical stimulus. These rules are two. First, it is necessary that the stomach should be clean, and that nothing shall gain entry to it from without. Such conditions were not formerly fulfilled.

It is true the stomach was emptied by removing the stopper from the fistular cannula, but it was not washed out till an acid reaction was no longer given, and consequently preformed gastric juice was left behind between the folds of the mucous membrane. At the same time saliva from the cavity of the mouth could gain entry, which quickly became acidified in the incompletely emptied and imperfectly washed-out organ. It is, therefore, not surprising that the glass tube, by setting up contractions of the stomach, was the means of expressing small quantities of acid fluid from the fistula-tube. (The relationship between mechanical stimulation and the motor functions of the stomach is not to be confounded with what we are here speaking of.) That matters are as I state, and that the facts correspond to the explanation is proved by this; namely, that nobody till now has obtained genuinely pure gastric juice of an acidity amounting to 0.5 or 0.6 per cent. It is only necessary to call to mind that Heidenhain, when determining the acidity of the juice first obtained from the resected stomach, was placed in no little doubt as to whether his results (0.5 to 0.6) were correct, and his assistant at the time (Gscheidlen) was set to verify the correctness of his standard solutions.