232 J. L. Jona: 



the excess of salt (and thus of necessity do work against osmotic 

 pressure), has not been determined, but the fact that the A 

 of the urine of seals recorded by Portier gives values of 0.73 

 to 3.5 seems to point to the fact that salts are absorbed and 

 excreted by the kidney, the urine probably having a I'W A 

 between meals and a high A during digestion, as suggested 

 bv Bottazzi (1), Bur in regard to land mammals in general 

 and man in particular, my own observations on the osmotic 

 pressure of liquid foods throw some light on the subject. 



It is generally admitted that one of the functions of the 

 stomach is the establishment of osmotic equilibrium between 

 the fluid food swallowed and the blood (3). This it does by 

 adding salts, etc., to hypotonic fluids, and by diluting the 

 hypertonic. In the latter function the action of the stomach 

 is aided by the salivary glands, which pour out a copious secret 

 tion of saliva. In one experiment cited in the appendix, 72 c.c. 

 of saliva were poured out in 15 minutes during the process of 

 chewing about 12 grms. of barley-sugar. 



This function is no doubt protective, for the deleterious 

 ejffects of exposing tissue cells to the action of hypertonic or 

 hypotonic fluids are well known. The swelling up of, and 

 interference with sensation in, and the function of the skin 

 after prolonged immersion in water, and on the other hand the 

 "roughness" produced when a piece of confectionery is retained 

 for a few minutes between the teeth and cheek, are common 

 examples. 



Of the foodstuffs ordinarily admitted to the stomach, the 

 great majority are in solid or gelatinous or colloidal form, and 

 to such substances the considerations of osmotic pressure cannot 

 apply. The actual fluid foods admitted to the stomach of man 

 are milk, the ordinary beverages, fruit juices" and beef teas, 

 meat extracts and soups, while in the case of the lower animals 

 in the natural state, the list is very much shortened, since the 

 ingestion of prepared foods is solely confined to man and the 

 domestic animals. In tea, coft'ee and cocoa there is usually a 

 sugar addition, which varies with the personal taste, but tl.e A 

 given by the contents of a cup of tea, as prepared for an 

 ordinary individual, was found to be about 0.46^0. Tlie A 

 of milk has been determined by many observers, and is the 



