An analogous experiment with bread was also carried out by Dr. Glinski. The eating of fresh moist bread produced no secretion worth mentioning, while dry bread, on the other hand, caused the saliva to flow in large quantities. The results of this experiment permit us to draw extremely instructive conclusions. In the first place, the several salivary glands are, as a matter of fact, very sharply differentiated in the conditions necessary for their activity - that is to say, in respect to the agencies which excite their nervous mechanisms. Secondly, the innervation apparatus of the parotid manifests a very sharp selective power in the choice, so to speak, of an adequate stimulus. The mechanical effect of large pieces of flesh is naturally much greater than that of the finely powdered material, and yet it was precisely to the latter that the glands responded. The stimulus is, therefore, not due to the mechanical, but to some other property of the food. This other property is obviously the dryness of the material. Our example illustrates how that which we may term "purposiveness" comes into play in the working of our glands and also how erroneous is the opinion that the mechanical stimulus is all potent.

Indeed, previous authors have already pointed out that dry substances cause a specially free secretion of saliva, and yet physiological opinion throughout the length and breadth of the land, as expressed in text-books, has chosen to recognise a universal instead of a specific excitability. Dr. Wulfson, who is at present carrying on the investigation of salivary secretion in our laboratory, has added a very interesting observation to the results of Dr. Glinski already related. The parotid gland, which is hardly, if at all, excited when one offers fresh meat to the animal, responds with a very active secretion, when dry food (bread or powdered meat) is offered. This phenomenon is all the more surprising since the desire of the animal for eating is much more strongly excited by flesh than by dry bread. I am quite convinced that an exact study of the exciting agencies of the three salivary glands will furnish a number of new data bearing upon the question in hand.

The second reagent which is poured out on the raw material in the digestive canal is the gastric juice. How, in the normal course of events, is the work of the gastric glands, which prepare this juice, called into play? With the first, and manifestly important factor, which has a relation thereto, you are already acquainted, and, indeed, have already seen. I refer to the production of gastric juice in the empty stomach, as a result merely of the swallowing of food in the so-called sham feeding of an cesophagoto-mised dog. When one takes into consideration the absolute independence of this factor, and the intensity of the effect, which makes itself evident in the secretion of a large quantity of juice of high digestive power, the exciting agency which brings about such secretion must be recognised as one of the most important and effective processes in gastric digestion. But in what does it consist? At first sight it appears - and when I previously drew your attention to the fact I expressed the opinion - that there is here a simple reflex effect from the cavity of the mouth upon the secretory nerves of the stomach, similar to the reflex excitation, e.g., of the parotid gland, by finely powdered flesh thrown into the mouth.

Now, however, I assert quite emphatically that this is not the case. We have, it is true, in the activity of the salivary glands an analogous phenomenon to indicate - not, however, that of which we have just spoken. We might apply every conceivable form of stimulus which could possibly come into play in the act of eating, and yet would not obtain the slightest indication of secretory activity in the stomach. In this dog with a gastric fistula, and with also a divided oesophagus, I will try such an experiment, using the most effective chemical stimulus to the buccal mucous membrane, viz., acid solution.

The secretion of saliva begins at once, as you see; the acid is, therefore, effective. From the stomach, however, in spite of continued excitation, no secretion results, although the acid, mixed with the saliva, is swallowed and flows out again from the upper segment of the oesophagus - that is to say, passes along precisely the same path that the food takes in sham feeding.

We could experiment in the same way with a number of other substances: saline, bitters, pepper (strong local excitation), mustard, and so on, and always with the same results; a free secretion of saliva, but perfect quiescence of the gastric glands. We may even, with the same object, employ the soluble constituents of flesh in the form of a decoction, and likewise observe, in most cases at least, no sign of activity on the part of the gastric glands.

With the chemical we may also combine a mechanical stimulus. We can, for example, wipe out the mouth with a sponge soaked in the solution to be experimented with, but always with the same negative result. We may finally give such pieces of sponge, or even smooth stones of considerable size, to the dog to swallow, passing them back behind the anterior pillars of the fauces and allowing them to fall out again, from the upper portion of oesophagus. It may be added that a well-taught dog puts up with all these procedures without the slightest protest. You see that all the manipulations in this case are carried out with bare hands and without instrumental aid. One can easily train a dog to swallow stones which are placed in the anterior part of the buccal cavity. It simply makes a few chewing movements and swallows them down. The dog on which the acid experiment has just been made serves also for the swallowing of the stones. The attendant now places some pebbles in the front part of the mouth, when the animal rolls them round, as if chewing and gnawing them, and then swallows them. The stones fall out, as you see, from the oesophagus, and drop with an audible sound upon the table.

This play with the stones has now lasted fifteen or twenty minutes (in the laboratory we have often kept it up for hours), and yet not a drop of gastric juice is to be seen.