DIGESTION IN THE SMALL INTESTINE. 409 



that proteids may be digested in pancreatic infusions with a neutral or 

 even faintly acid reaction ; it even appears that in the case of the pig 

 the pancreatic infusion is only active in digesting proteids when the 

 intestinal reaction is acid. 



As already mentioned, the pancreas is not under every condition 

 capable of forming a secretion which will digest proteids, and under 

 many circumstances infusions of the pancreas will be entirely inert on 

 proteids. This would seem to indicate that while trypsin, or the proteo- 

 lytic ferment, is formed in the cells of the pancreas, it is preceded by 

 another substance termed zymogen, which is gradually in the normal 

 conditions of the gland converted into trypsin. In support of this state- 

 ment it may be mentioned that the pancreas obtained from the slaughter- 

 house or from fasting dogs is often inactive, while the most activity is 

 present about four or seven hours after feeding. It is supposed that the 

 zymogen, which is soluble in water and glycerin, and which is found in 

 the inner zone of the secretory cells, is, through the gradual action of 

 oxygen, converted into trypsin. This conversion normally occurs in the 

 interior of the gland during digestion, but even" inactive glands may de- 

 velop trypsin through exposure to the air after death or by the action of 

 dilute acetic acid. 



SchirT and Herzen claim that there is a close connection between the 

 action of the spleen and the development of trypsin, and they claim to 

 have demonstrated that the pancreas of an animal from whom the spleen 

 has been removed is incapable of digesting proteids, and that if such a 

 pancreas be rubbed up with a portion of spleen it will then acquire the 

 power of digesting proteids. This statement, however, needs further 

 confirmation. 



When the pancreatic digestion of proteids is prolonged, in addition 

 to peptones, various other bodies make their appearance. Lencin and 

 tyrosin appear in large amounts, with traces of asparaginic acid, xanthin, 

 and a bod}- which is . colored red with chlorine- or bromine-water. The 

 longer the pancreatic digestion is prolonged, the larger will be the amount 

 of lencin and tyrosin present and the smaller the amount of peptone ; 

 from which it would appear that these crystalline substances result from 

 the gradual breaking down of the peptone itself. 



Kiihne explains this result b} r supposing that the albuminous bodies 

 under the action of trypsin become converted into two forms of peptone, 

 to which the terms respectively antipeptone, which does not undergo 

 further change, and hemipeptone, the latter in normal digestion being 

 converted into leucin, tyrosin, etc., and readily undergoing putrefaction, 

 resulting in the formation of indol, skatol, and phenol. 



If a pancreatic digestive mixture be neutralized so as to precipitate 

 alkali albumen, and then treated with an excess of alcohol, the greater 



