Finally, I am able to demonstrate to you the following instructive experiment. In the presence of some of my listeners, whom I had invited to attend an hour before the lecture, I carried out the following procedures on two dogs, both of which had ordinary gastric fistulæ and were, besides, œsophagotomised. Into the stomach of one, while its attention was distracted by patting and speaking kindly to it in order to avoid arousing any thoughts of feeding, a definite number of pieces of flesh were introduced through the fistula. The morsels were threaded on a string, the free end of which was fastened to the fistular cannula by inserting a cork. The dog was then brought into a separate room and left to itself. A like number of pieces was introduced into the stomach of the other dog in the same way, but during the process a vigorous sham feeding was kept up, the animal being afterwards left alone. Each dog received 100 grams of flesh. Since then an hour and a half have elapsed, and now we may draw the pieces of flesh out by means of the thread and weigh them. The loss of weight, and consequently the amount of flesh digested, is very different in the two cases. In that of the dog without sham feeding the loss of weight amounts to merely 6 grams, while the flesh withdrawn from the stomach of the other dog weighs only 70 grams, that is to say, was reduced by 30 grams. This, therefore, represents the digestive value of the passage of food through the mouth, the value of an eager desire for food, the value of an appetite.
I give also a series of figures obtained by Dr. Lobassoff in analogous experiments. Into the dog’s stomach 25 pieces of flesh (100 grams) were brought. The flesh remained two hours in the cavity. Without sham feeding 6.5 per cent, with eight minutes’ sham feeding 31.6 per cent, of the quantity was digested.
Again: the flesh remained an hour and a half in the stomach; without sham feeding 5.6 per cent, with five minutes’ sham feeding 15 per cent, was digested.
Once more: the flesh remained five hours in the stomach; without sham feeding 58 per cent, with sham feeding 85 per cent, was digested, the balance of undigested food being 42 per cent in the one case and 15 per cent in the other.
I must, however, add that from the nature of this experiment it is not well adapted for class demonstration, and may often fail. On the one hand, it is not at all easy to conceal the introduction of the flesh from the dog; on the other, the unusual and distracting surroundings of the animal often causes a short period of sham feeding to have less effect than would otherwise pertain. In order to avoid such failures it is better before an audience to carry out this experiment only on dogs accustomed to appear in the lecture theatre, and of whose temperament the experimenter is well assured.
I hope you have now been convinced of the great importance which is to be attached to the passage of food through the mouth and œsophagus, or, in other words—and this, according to our former experiences, means the same thing—to the eager desire for food. Without this longing, without the assistance of appetite, many forms of food-stuffs which gain entry to the stomach remain wholly devoid of gastric juice. Others, it is true, excite a secretion, but the juice poured out is scanty and weak.
It is only later, when we have still more fully recognised the conditions upon which the secretory work of the gastric glands depends, that we shall be able to grasp the meaning of these facts in a more comprehensive manner. For instance, why does bread brought unnoticed into the stomach of the dog cause no secretion for hours, while flesh tolerably soon (after twenty to forty minutes) provokes this act? This will be explained in the next lecture; now, however, we must consider other questions.
How long does the after-effect, the echo of the first impulse to the secretory nerves of the stomach, continue to last? How long does appetite juice continue to flow after the normal act of eating, which, especially in the case of animals, is not of long duration? We have already determined many times, not only on our dog with the isolated stomach, but also on other animals, how long the after-effect of sham feeding is continued.
Here, for example, is an experiment from the article of Professor Ssanozki which deals with the point. The dog had a gastric fistula and also an opening leading into the œsophagus. After a sham feeding of five minutes the secretion began, and was continued as follows:
| Time in minutes. | Quantity. | Digestive power. |
|---|---|---|
| c.c. | mm. | |
| 10 | 25.5 | 8.1 |
| 10 | 20.0 | 8.0 |
| 10 | 13.5 | 6.8 |
| 10 | 11.0 | 7.5 |
| 10 | 8.5 | 8.1 |
| 10 | 6.5 | 9.0 |
| 20 | 13.5 | 7.4 |
| 20 | 11.0 | 7.2 |
| 20 | 7.0 | 7.2 |
| 20 | 11.5 | 6.8 |
| 20 | 11.0 | 6.5 |
| 30 | 6.5 | 7.6 |
| 20 | 5.5 | 7.2 |