And yet the feather and the glass tube continue the even tenor of their ways to this moment and function in some text-books, yea, even in articles which specially treat of gastric secretion as exciters of the gastric glands. There are, it is true, a few physiologists who hold mechanical stimulation, in relation to gastric secretion, not to be very effective, and give it a subordinate position in the series of exciting agencies, but as yet I know of no other physiologist who has wholly denied its influence, and who has not held it possible to obtain at least some juice by it.
To conclude this lecture, we will take into consideration a question connected with the matter we have just discussed. Since the contact of food with the gastric mucous membrane has no direct influence on the secretion, is its entry into the stomach devoid of all connection with the secretory process?
It can hardly be doubted that, under normal conditions, the stomach is the seat of certain definite sensations, that is to say, its surface has a certain degree of tactile sensibility. This sensation is, as a rule, very weak, and the majority of people become accustomed to pay no heed to it in the normal course of digestion. They obtain their sensations of general well-being, and especially of satisfaction from the enjoyment of food, without taking cognisance of the factors contributing to them. The feeling of general hunger, however, is referred solely to the stomach.
On the other hand, all of us have met with men who could describe exactly, and with gusto, how they were able to follow a special tit-bit, or a mouthful of a favourite wine, the whole way through the œsophagus down to the stomach, especially when the latter happened to be empty. Naturally the gourmand, who directs his attention continuously to the act of eating, can in the end distinctly perceive sensations, and even call them up to the consciousness, which in other people are normally masked by other sensations and impressions. We may therefore take it that the satisfaction derived from eating is caused not only by stimulation of the mouth and throat, but also by impulses awakened by the passage of the food along the deeper portions of the œsophagus and by its entry into the stomach. In other words, food which merely passes through the mouth and throat produces less enjoyment and excites, therefore, a less feeling of appetite than the food which passes the whole way into the stomach. The appetite, the eager craving after food, is, indeed, a very complex sensation, and often not merely the need of the organism for food material is necessary for its excitement, but also a condition of thorough well-being, together with a normal healthy feeling in all parts of the digestive tract. For this reason it is easy to understand how patients who have diseased sensations in these organs, and who have no feeling of appetite, no desire for food, remember the sensations, whether consciously or unconsciously, even when they are no longer present. Cases are known to neuro-pathologists where people with gastric anæsthesia suffered from this loss of appetite. Such patients are no longer conscious of having stomachs, and dislike the idea of eating because the food, as they express it, appears to fall into a strange empty sack. In this way one can also conceive how the appetite becomes lost in cases of long-continued obstruction of the alimentary tube. The patients forget their stomachs, and in such instances direct introduction of food into the organ, after an operation, may suddenly bring back the appetite.
As a further illustration, I may be permitted to give an instance from my own personal experience. After an illness with which a transient but high fever was associated, although otherwise fully recovered, I had lost all desire for food. There was something curious in this complete indifference towards eating. Perfectly well, I only differed from others in that I could with ease abstain from all food. Fearing that I should collapse, I resolved on the second or third day to endeavour to create an appetite by swallowing a mouthful of wine. I felt it quite distinctly pass along the œsophagus into the stomach, and literally at that moment perceived the onset of a strong appetite. This observation teaches that the tactile sensation of the stomach at the moment of entry of food is capable of awakening or increasing the appetite. It is known that withholding food from the organism, or in other words the creation of a necessity for food, does not lead immediately, nor in all cases, to the production of an appetite, to a passionate craving for food. How often does it happen that the ordinary hour for a meal has struck, and yet, owing to some keenly interesting occupation, not the least desire for food is felt? It is known to everybody, indeed it has become a proverb, that real appetite first sets in with eating. If this be true, the initial impulse towards awakening an appetite may originate in the stomach and not in the buccal cavity. When we spoke above of the desire for food being the excitant of the secretory nerves of the stomach, we naturally meant the passionate and conscious longing for food, that which is called “appetite,” and not the latent need of the organism for nourishment, the lack of nutrition, which has not yet been transformed into a concrete passionate desire. A good example which enables us to differentiate between these two factors is furnished by our dogs with sham feeding. The necessity for food exists in such cases even before the experiment; the juice, however, only begins to flow as soon as this need has taken the form of a passionate longing. It is therefore quite possible that in the case of some dogs, and at a certain stage of hunger, the touching of the gastric mucous membrane with any object at hand, its mechanical excitation, its distension by the food mass, may give the impulse which excites the appetite, and when the appetite is awakened the juice flows. This is possibly a third reason why, in the old experiment, the mechanical stimulus came to be considered effective. Viewed from this point it may, to a certain degree, lead to a reconciliation between my assertion concerning the inefficiency of the mechanical stimulus and the generally prevailing belief. I further also admit that mechanical excitation will at times call into play the work of the gastric glands, not however directly by means of a simple physiological reflex, but indirectly, after it has first awakened and enlivened the idea of food in the dog’s consciousness, and thereby called forth the passionate desire. I hope that the foregoing will in no way lead to a confusion of ideas in your minds, but will assist you to an exact and concrete analysis of the previous simple explanation of the facts. This representation, which bears more or less of a hypothetical character, could, of course, be submitted to experimental proof. For such it is only necessary to compare the influence which sham feeding exercises in an œsophagotomised dog with that in one having a simple gastric fistula.
LECTURE VIII
PHYSIOLOGICAL ACTION AND THE TEACHING OF INSTINCT: EXPERIENCES OF THE PHYSICIAN
It would be desirable, in the interests of medicine, that the methods described in these lectures should be employed in experimental investigations into the pathology and therapeutics of the digestive canal on the lines laid down—The fact that the beginning of the secretory work in the stomach depends upon a psychic effect harmonises with the experiences of every-day life, namely, that food should be eaten with attention and relish—To restore the appetite has from all ages been the endeavour of the physician—The indifference of the present-day physician towards appetite—Probable causes of this—Curative remedies based upon a restoration of appetite—The therapeutic effects of bitters depend upon the excitation of appetite—The usages of the mid-day meal are in agreement with physiological requirements—Physiological reasons for certain instinctive customs and empirical regulations—Importance of an acid reaction of the food—Dietetics of fat and its therapeutic application—The peculiar position of milk among food-stuffs is based on physiological reasons—Explanation of the curative effects of sodium bicarbonate and sodium chloride—The causes of individual differences in the work of the digestive glands—Participation of the inhibitory nerves of secretion in the production of pathological effects.
Gentlemen,—To-day we shall endeavour to bring the previously communicated results of our laboratory investigations into reconciliation with the customs observed in the ingestion of food, and with the regulations prescribed by the physician in disorders of the digestive apparatus. To bring our knowledge to full fruition, and so secure for it the most useful application, the same methods should be applied from the same standpoint to the experimental investigation of the pathology and therapeutics of the alimentary canal. Nor should we be likely to encounter insuperable difficulties. Thanks to the advances of bacteriology, many of the pathological processes can now be experimentally produced in the laboratory. Moreover, we would, in a sense, have to deal with external ailments, since our present methods enable us to obtain access to any desired part of the inner surface of the digestive canal. In such pathological animals the functional diseases of the apparatus could be studied in a precise and detailed manner; that is to say, the alterations of secretory activity, the properties of the fluids, and the conditions under which they appear could be examined. On such animals therapeutic remedies could also be tested, the whole process of healing and the final result experimentally observed, while the conditions of secretory activity during every phase of the healing process could be investigated. It can hardly be doubted that scientific, that is to say ideal, medicine, can only take its proper position as a science when, in addition to an Experimental Physiology and Pathology, there has also been built up an Experimental Therapeutics. A proof that this is possible is furnished by the recent vigorous strides made by the science of bacteriology.
I have already described one of such pathological therapeutic experiments; namely, on the dog whose vagi nerves were divided in the neck. Other similar cases I can also call to mind. Our dog with the two stomachs suffered at one time from a slight and transitory gastric catarrh. It was then very interesting to observe that the pathological process (which we were usually able to wholly guard against) spread from the large to the small stomach. It manifested itself here in an almost continuous slimy secretion of very slight acidity, but of strong digestive power. At the beginning of the ailment, indeed before it became fully established, the psychic stimulation was remarkably effective (that is to say, still furnished juice in appropriate quantity), while local excitants almost completely failed. One may conceive that the deeper layers of the mucous membrane with the gastric glands were still healthy, and thus easily thrown into activity by central impulses, whilst the surface of the membrane with the end apparatus of the centripetal nerves was already distinctly damaged. I mention these, which I may call impressions rather than precise observations, because I wish to point out what a fruitful field awaits the investigator who wishes to study, with the aid of our present methods, the pathological conditions of the digestive organs and their treatment. Such an investigation is all the more desirable because clinical study of the same subject (notwithstanding the zeal devoted to it during the last ten years and the results derived therefrom) has to contend with serious difficulties. We must not forget that the sound or stomach-tube, the chief clinical instrument, is more uncomfortable than the ordinary form of gastric fistula which was previously practised on animals, and yet the physiology of the stomach, even with the aid of the latter, made no material progress for many long years. Nor is this difficult to understand. The investigator obtained through the fistula a mixture of substances from which it was difficult, or even at times impossible, to decide anything.
Hence the exact scientific study of therapeutic questions in this region still belongs to the future. But this does not exclude the probability that the newer acquirements of physiology may fruitfully influence the work of the physician. But physiology naturally can make no pretence to guide the field of medicine, since the knowledge at its disposal is incomplete and is much more restricted than that of the broad world of clinical reality. As a recompense for this, however, physiological knowledge is often able to explain the causation of an illness and the meaning of empirical curative methods. To employ a remedy the mode of action of which is not clear is quite a different thing from knowing precisely what we are doing. In the latter case the treatment of the diseased organ will be more effective because it will be better adapted to the special needs of the case. It is thus that medicine, being daily enriched by new physiological facts, will at length grow into what it ideally must become; namely, the art of repairing the damaged machinery of the human body, based upon exact knowledge, or, in other words, applied physiology.