We have already seen that no other excitant of gastric secretion, so far as quantity and quality of the juice are concerned, can compare with the passionate craving for food.

To a certain degree we can understand - and this contributes to an explanation of matters - how medical science of our time has come to regard so lightly the loss of appetite as a special object for treatment. Now, however, the experimental method has penetrated more and more into medical science, with the result that many pathological factors and therapeutic agents are judged of according to whether they hold good in the laboratory or not - that is to say, they are valued only in so far as they can be verified by laboratory experiments. Naturally we do not doubt that a movement in this direction indicates a great advance, but even here, as with every undertaking of mankind, things do not proceed without mistakes and exaggerations. We must not consider an event to be a mere picture of the imagination because it is not realisable under given experimental conditions. We often do not know all the essential conditions for the production of the phenomenon in question, nor are we yet able to grasp the connection between all the separate functions of life as fully as may be desired.

Thus in the clinical treatment and pathology of digestion assistance was sought for in the laboratory, but nothing was there met with which had a relation to appetite, and consequently this factor was overlooked in medical practice. As stated above, the psychic gastric juice obtained only cursory mention in physiology, and this not even by all authors; and when it was noticed it was related more as a curiosity. Great importance was, on the other hand, assigned to the mechanical stimulus, the efficiency of which, now that our knowledge is more complete, has been shown to be purely imaginary. Each of the contending factors has at length been assigned its proper place, and if clinical medicine maintains her worthy desire of following out the experimental investigation of her problems, she must in actual practice accord to appetite its old claim for consideration and treatment.

But notwithstanding the indifference of physicians to appetite in itself, many therapeutic measures are based on the promotion of it >And in this the truth of empiricism makes itself irresistibly felt. When the patient is enjoined to eat sparingly, or when he is restrained from eating at all till the physician expressly permits, or again, when he is (for instance, during convalescence) removed from his ordinary surroundings and sent to an establishment where the whole life, and particularly the eating, is regulated according to physiological needs - in all these cases the physician seeks to awaken appetite, and relies upon it as a factor in the cure. In the first case, where the food is prescribed in small portions, in addition to preventing the overfilling of a weak stomach, the oft-recurrence of appetite juice, which is so rich in quantity and so strong in digestive power, is of great importance. I ask you here to call to mind one of our experiments in which food was given in small portions to a dog, and thus led to a secretion of much stronger juice than if the whole ration had been eaten at once. This was an exact experimental reproduction of the customary treatment of a weak stomach.

And such a regulation of diet is all the more necessary, since, in the commonest disorders of the stomach, only the surface layers of the mucous membrane are affected. It may, consequently, happen that the sensory surface of the stomach, which should take up the stimulus of the chemical excitant, is not able to fulfil its duty, and the period of chemical secretion, which ordinarily lasts for a long time, is for the most part disturbed, or even wholly absent. A strong psychic excitation, a keen feeling of appetite, may evoke the secretory impulse in the central nervous system and send it unhindered to the glands which lie in the deeper as yet unaffected layers of the mucous membrane.

An instance of this, taken from the pathological material of the laboratory, I have already related at the beginning of this lecture. It is obvious in these cases that the indication is to promote digestion by exciting a flow of appetite juice, and not to rely upon that excited by chemical stimuli. From this point of view the meaning of removing a patient, the subject of chronic weakness of the stomach, from his customary surroundings is also plain. Take, for instance, a mentally overstrained individual, or a responsible official; how often does it happen that he cannot for a moment distract his thoughts from his daily work. He eats without noticing it, or eats and carries on his work at the same time. This often happens, particularly in the case of people who live in the midst of the incessant turmoil of great cities. The systematic inattention to the act of eating prepares the way for digestive disturbances in the near future, with all their consequences. There is no appetite juice, no "igniting juice," or, at most, very little.

The secretory activity comes slowly into play; the food remains much longer in the digestive canal than is necessary, or passes, for want of sufficient digestive juices, into a state of decomposition which irritates the mucous membrane of the alimentary canal and brings it into a condition of disease. No medicinal treatment can help such a patient while he remains surrounded by his old conditions. The fundamental cause of his illness still continues in progress. There is only one course to pursue; namely, to take him completely away, to free him from his occupation, to interrupt the interminable train of thought, and to substitute for a time, as his only object in life, the care of his health, and a regard for what he eats. This is attained by sending the patient to travel, or by placing him in a hydropathic establishment. It is the duty of the physician to regulate not only the life of individual patients according to such rules, but also to have a care that in wider circles of the community a due conception of the importance of eating should be disseminated. This is particularly so with the Russian physician.