GASTRIC JUICE

a colorle acid fluid, secreted by certain cells in the stomach, containing enzymes and hydrochloric acid in addition to small amounts of organic and inorganic materials. The principal enzyme, or ferment, present, is pepsin, which is derived from a precursor, pro pepsin. The latter, on coming into contact with acid, is converted into the ferment which acts upon the protein of the food. Pepsin, therefore, can only act in acid solution, and both the ferment itself and the hydrochloric acid of the G.J. are secreted by special cells in the stomach. ‘The amount of the secretion, and also its composition, are determined by the nature of the food. Pepsin acts on protein matter, converting it into soluble forms, albumoses and peptones, which are pa ed on to the intestine, there to undergo further change. It is po ible that another ferment, rennin, is also present in G.J.; this is, however, doubtful, as the clotting of milk may be due to the pepsin.