ALBUMINS OR PROTEINS. 203 



Let us now return to the relations of the animal organism to the albu- 

 mins it obtains in its food. They are not at all attacked by saliva, with 

 which they first come into contact. This secretion does not contain any 

 ferment which can act upon the proteins. 



The albumins are next subjected to the action of pepsin in the stomach. 

 Spallanzani * was the first to give a clear demonstration of the digestive 

 action of the gastric juice. Normal gastric juice reacts acid. It contains 

 free hydrochloric acid. This was definitely established by Bidder and 

 Karl Schmidt. 2 They estimated quantitatively the total chloride present 

 in the stomach, and also all the .bases, potash, soda, lime, magnesia, 

 iron oxide and ammonia, and found after computing the amount of 

 hydrochloric acid required to combine with these, that some remained 

 uncombined. We shall discuss the composition of gastric juice and its 

 secretions more in detail later, confining ourselves at present to the state- 

 ment that the proteolytic ferment mentioned, i.e. pepsin, is only active 

 when in acid solution. It was first believed that the pepsin was united 

 with the hydrochloric acid and exercised its functions as pepsin-hydro- 

 chloric acid. It was, however, soon shown that the hydrochloric acid 

 could, on the one hand, be substituted by other acids, for instance, lactic 

 acid, while, on the other hand, other acids did not replace the hydrochloric 

 acid in equivalent amounts. The amount of hydrochloric acid in the gas- 

 tric juice is very appreciable. The gastric juice of dogs contains 0.5-0.6 

 per cent hydrochloric acid; that of cats 0.5 per cent; while for human beings 

 from 0.2-0.3 per cent is reported. The attempt has been made to assign 

 to the hydrochloric acid content of the stomach an antiseptic action as 

 its greatest function. Although there is undoubtedly such an action, the 

 fact also remains that hydrochloric acid participates in the digestion of 

 albuminous substances. The mechanism of its activity has, however, not 

 been thoroughly explained. It may be summed up as follows : If we add 

 hydrochloric acid, or even gastric juice, to albumin, a peculiar change 

 takes place. The albumin swells up and fills the entire vessel as a gel- 

 atinous mass. Large amounts of hydrochloric acid are simultaneously 

 combined. The quantity of free hydrochloric acid diminishes. We can 

 imagine that the hydrochloric acid enters into combination with the albu- 

 min, producing soluble albumins, the so-called " acid-albumins." It is 

 possible that the hydrochloric acid loosens up the albumin molecule, i.e., 

 changes it in some way, preparing it for the action of pepsin. There are, 



1 Versuche iiber das Verdauungsgeschaft. German by Michaelis. Leipsic, 1785. 

 Eberle: Physiolog. Verdauung auf natiirlichem und kiinstlichem Wege Wurzburg, 1834. 

 Cf. also Gamgee: Physiologische Chemie der Verdauung: Leipsic and Vienna, 1897. 

 W. Beaumont : Neue Versuche und Beobachtungen iiber den Magensaf t und die Physi- 

 ologic der Verdauung. German by B. Luden. Leipsic, 1834. 



2 Bidder and Schmidt: Die Verdauungssafte u. d. Stoffwechsel, Mitau u. Leipsic, 

 1852. 



