190 THE PROCESSES OF DIGESTION AND RESORPTION. 



press. Pressings and extract are united and treated with a saturated 

 solution of ammonium sulphate, in the proportion of three volumes 

 of the salt solution to three of the extract. A heavy precipitate 

 results on standing, which is filtered off, suspended in water, and 

 dialyzed. The greater portion of the albumins remains undissolved, 

 while a smaller amount together with the ferment passes into 

 solution. The residue is again extracted, the extracts are united, and 

 dialyzed free from the sulphate (three to four days). This solution 

 is quite active and rapidly changes albumoses and peptones into 

 material which no longer gives the biuret reaction and is in great 

 part precipitated by phosphotungstic acid in crystalline form. 



The ferment is destroyed by boiling, and is much impaired in 

 its activity by exposure to a temperature of 63 C. for two hours. 

 It decomposes peptone (albumoses) in feebly alkaline or neutral 

 media, while it is inactive in an acid medium. Acetic acid does 

 not destroy the ferment within one hour. Prolonged contact with 

 hydrochloric acid (of course, always in dilute solution) seems to 

 destroy it. Alcohol impairs its activity very materially. 



Among the products of decomposition resulting from the action 

 of erepsin on syntonin Cohnheim obtained arginin, lysin, histidin, 

 leucin, tyrosin, and ammonia. We now know that all the other 

 cleavage products to which trypsin gives rise also appear with 

 erepsin. Especially important is the fact that the amount of am- 

 monia which is obtained on distillation with magnesia from the 

 mixture of decomposition-products is the same as is obtained on 

 decomposition with acids, as also with trypsin, showing that the de- 

 composition of the nitrogenous molecule does not extend beyond the 

 stage of ami no-acids. 



As regards the action of erepsin on the various albumoses and 

 peptones, Cohnheim ascertained that they are all decomposed by 

 the erepsin to the point where the biuret reaction is no longer 

 obtained ; though with varying rapidity. The native albumins are 

 in no ways affected, but, very curiously, casein is decomposed. 

 This is noteworthy in view of Gmelin's observation that suckling 

 dogs secrete no pepsin. 



The protamins are decomposed entirely like the albnmoses and 

 peptones, while the histons are only affected in part, which coin- 

 cides with the position which the histons occupy midway between 

 the protamins and the true albumins. 



While Cohnheim assumes that the activity of erepsin is mainly 

 displayed within the cells of the intestinal mucosa, there is some 

 evidence to show that a portion of the ferment is secreted into the 

 lumen of the gut and may thus become active outside of the cells 

 also (Salaskin). 



To demonstrate the action of erepsin, it is only necessary to add 

 from 15 to 20 c.c. of an extract of the intestinal mucosa, prepared 

 as described above, to a small amount of a solution of peptone 

 (Witte), and to test every ten to fifteen minutes for the biuret reaction. 



