VALUE OF THE INSTINCTIVE CRAVING FOR FOOD. 129 



excitable, without distinction, by every mechanical, chemical or thermal 

 agency, independent oF the speciality which attaches to each single phase 

 of digestion. According to the prevailing view of matters, the pro- 

 nounced action of those agencies could serve merely as favouring or 

 restraining influences, and not as normal definite guiding factors in the 

 secretory work of digestion. Instead of a crude indefinite scheme, we 

 see now the outlines of a skilled mechanism which, as with everything 

 in nature, proves itself to be adapted with the utmost delicacy and in 

 the most suitable manner to the work which it has to perform. 



An essential advantage to the digestive process is derived from the 

 instinctive craving for food ; for, in addition to the impulse to seek out 

 and partake of food, the instinct is at the same time the first and 

 strongest exciter of several digestive glands. The fluids of varying 

 reaction, secreted under its influence, convert a considerable part of the 

 food into a soluble half-fluid condition, and thus allow the chemical 

 constituents of the food-mixture to take effect. In consequence of this, 

 the initial rate of gland activity is modified to harmonise with the altered 

 constituents of the food, which are now in such a condition that they 

 are capable of acting directly upon the end organs of the neuro-secretory 

 apparatus. In the interest of all the constituents a certain equilibrium 

 is established, in regard both to the quantity and strength of the 

 digestive fluids as a whole ; the one ingredient is promoted, the other 

 to a certain degree restrained : a species of contest for the ingredient 

 needed is fought out between the several components of the food. The 

 secretory work which began with the ingestion of food is thus propa- 

 gated farther and farther along the alimentary canal, thanks to a 

 suitable interlinking of the several processes. 



In my address before the Association of Russian Medical Men, to 

 which I referred in the beginning of these lectures, I expressed the 

 opinion that in ten years we should have as good a knowledge of the 

 chemical work of the digestive canal as we have now of the physical 

 apparatus of the eye. Since then two years have fled, and, when 1 look 

 back upon their results, I see no reason to retract my words. Even in 

 the Far West a lively interest is taken in our researches, and with the 

 assistance of numerous European colleagues together with our workers 

 here, the investigations, when once started on the right way, will rapidly 

 lead to a complete accomplishment of the task. We are not dealing with 

 questions concerning the nature of life or the physics and chemistry 

 of the cell. The working out of these presumably will furnish, for a 

 long series of generations, a theme of engrossing but ever-insatiable 

 interest, before the final solution of the problem is arrived at. In 

 our department of life, however, that is, in organ physiology, as we 

 may say in contrast to cell-physiology, one may reasonably hope that 



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