242 DIGESTION. 



grammes of water. They found that the fluid thus prepared, containing four times the 

 normal proportion of saline principles, did not possess by any means the energy of action 

 on alimentary substances of the normal secretion. These facts have led physiologists to 

 attach little importance to the ordinary saline principles found in the gastric juice. 



In the various analyses of the pure juice from the human subject and the inferior 

 animals, particularly dogs, chemists have discovered the chlorides of sodium, calcium, 

 potassium, and ammonium, the phosphate of lime (necessarily in the form of the 

 biphosphate), magnesia, and a small proportion of phosphate of iron. Of these princi- 

 ples, the chloride of sodium has always been found to exist in greatest abundance. 



Action of the Gastric Juice in Digestion. 



In treating of the composition of the gastric juice, frequent allusion has been made to 

 its solvent action in digestion and to the constituents on which this property depends. 

 Certain of the principles most readily attacked by this fluid are acted upon by weak acid 

 solutions containing no organic matter ; but, although some physiologists have been dis- 

 posed to regard the processes of solution which take place in the stomach as dependent 

 merely on the presence of a free acid, it is now well established that the presence of a 

 peculiar organic principle is an indispensable condition to the performance of real diges- 

 tion by the gastric fluid. It has also been fully established that fluids containing the or- 

 ganic principle of the gastric juice have no digestive properties unless they also possess 

 the proper degree of acidity ; and it is as well settled that fluids containing acids alone 

 have no action on albuminoids similar to that which takes place in digestion, and that 

 when these principles are dissolved by them it is simply accidental. 



It is a curious fact that the presence of any one particular acid does not seem essen- 

 tial to the digestive properties of the gastric juice, so long as the proper degree of acidity 

 is preserved. In the experiments of Bernard, Villefranche, and Barreswil, after saturating 

 the gastric juice with neutral phosphate of lime and adding acetic, phosphoric, or hydro- 

 chloric acid in such quantity that it certainly existed in a free state, the digestive proper- 

 ties of the fluid were retained. These authors regard it as essential that the normal acid 

 of the gastric juice should be thus capable of being replaced indifferently by other acids ; 

 for, they say, in case any salt were introduced into the stomach which would be decom- 

 posed by the lactic acid of the gastric juice, digestion would be interfered with, unless the 

 liberated acid could take its place. It can readily be appreciated that transient disturb- 

 ances might occur from this cause, were the existence of any one acid principle indispen- 

 sable to the digestive properties of the gastric juice ; while, if only a certain degree of 

 acidity were required, this condition might be produced by any acid, either derived from 

 the food or secreted by the stomach. 



Enough has already been said, under the head of the organic principle of the gastric 

 juice, to show that the presence of this substance is likewise a condition indispensable to 

 digestion. 



As far as has been ascertained by experiments upon artificial digestion, the mucus, 

 which always exists in greater or less quantity in the stomach, does not seem to be im- 

 portant. It is usual in these experiments to separate mucus and extraneous matters from 

 gastric juice by filtration before it is used; and the digestive properties of the fluid thug 

 treated are not sensibly affected when the mucus is allowed to remain. 



In studying the physiological action of the gastric juice, it must always be borne in 

 mind that the general process of digestion is accomplished by the combined, as well as 

 the successive action of the different digestive fluids. The act should be viewed in its en- 

 semble, rather than as a process consisting of several successive and distinct operations, in 

 which different classes of principles are dissolved by distinct fluids. The food meets with 

 the gastric juice, after having become impregnated with a large quantity of saliva ; and it 

 passes from the stomach to be acted upon by the intestinal fluids, having imbibed both 

 saliva and gastric juice. By studying the different digestive fluids in too exclusive a 



