Osmotic Equilibratiov. 238 



game as the blood, 0.57-0.59. Of all the fluid foods admitted 

 to the stomach of man, alcoholic beverages and fruit juices 

 alone are hypertonic. In fact most of the fluid foods admitted 

 to the stomach are hypotonic, thus containing a water excess 

 which the organism readily avails itself of for purposes of 

 •■ flushing out " the system, and which also allows of the addi- 

 tion of hydrochloric acid in the stomach. Moreover, it may 

 be safely stated that in no case is a fluid admitted in which the 

 hypertonicity is due to the mineral ingredients alone, except 

 under protest. The sense of taste stands at the entrance to 

 our alimentary canal, and tests the food not only qualitatively 

 but also quantitatively from the standpoint of molecular con- 

 centration. To this function of the sense of taste we may give 

 the name osmotactic, and it is undoubtedly to the possession 

 by the sense of taste of this osmotactic character that the 

 stomach mucosa is shielded from exposure to foods whose 

 osmotic pressure is far above that of the environment to which 

 the cells are normally accustomed. When for any reason a 

 highly hypertonic fluid is admitted to the stomach, then vomit- 

 ing (or sometimes diarrhoea) is the result. This is well seen 

 after the ingestion of strong salt solutions, large quantities of 

 sweetmeats or strong peptone solutions, or over-indulgence in 

 alcoholic or strongly saccharine beverages. In the process of 

 mastication and swallowing, the salivary glands are stimulated 

 to the pouring out of a copious secretion, and the organism has 

 developed here, too, another mechanism to aid in the dilution 

 of the stomach contents — namely, the sense of thirst, the 

 proper satisfaction of which, by the ingestion of a sufficient 

 quantity of water, tends to the dilution and consequent lowering 

 of the osmotic pressure of stomach contents. If these protec- 

 tive mechanisms fail in carrying out their object, then the 

 organism responds by rejecting the contents of the stomach 

 altogether by the reflex mechanism of vomiting. 



Thus in man. at any rate, and undoubtedly in the case of 

 the other mammals, the maintenance of a constant osmotic 

 pressure of the blood by means of the kidneys and excretory 

 organs is in a remarkable manner and to a considerable degree 

 aided by the possession by these higher animals of the senses 

 of taste and thirst. (Of man and nuimmals we can speak with 



