ELEMENTARY PHYSIOLOGICAL CHEMISTRY 227 



EXPERIMENT I. A solution of pancreatic extract in 1 per cent, 

 sodium carbonate solution is prepared (Liq. Pancreaticus, Benger, 

 diluted 30 times with 1 per cent, sodium carbonate solution). In order 

 to study the action of this on proteids, add to it a piece of fibrin which 

 has been soaked over night in 1 per cent, sodium carbonate solution, 

 and place on a water-bath at body temperature. 



The following points of difference may be noted between this and 

 the peptic digestion of fibrin: (1) The reaction is alkaline; (2) There 

 is no preliminary swelling of the fibrin, it is gradually eaten away 

 (erosion) ; (3) When the piece of fibrin has nearly disappeared remove a 

 sample of the digest, and neutralise with weak acetic acid. A pre- 

 cipitate of alkali albumin results (for Reactions, see p. 177). 



Apply to another sample the tests for proteoses and peptones, and 

 note that they are positive. 1 



EXPERIMENT II. If the pancreatic extract in Experiment I. be 

 boiled before the fibrin is added, no digestion will result. The digestive 

 agency is, therefore, a ferment which is destroyed by heat. 



EXPERIMENT III. Repeat Experiment I., making the reaction acid 

 by hydrochloric acid. Note that, although the fibrin becomes swollen 

 up as this depends on the acid, not on the ferment no formation of 

 proteoses or peptone occurs. The trypsin cannot act in acid medium. 



(4) Trypsin can carry digestion a stage further than can pepsin. 



EXPERIMENT IV. A minced pancreas has been macerated with 1 per 

 cent, sodium carbonate solution, and to the resulting preparation were 

 added the whites of several eggs. The mixture was then divided into 

 two parts, to one of which a few crystals of the antiseptic thymol were 

 added. Both were placed in the incubator for several days. 2 After 

 this time it will be noticed that the portion to which no thymol was 

 added has a very faeculent odour, and that this is absent from the 

 other portion. The odour is due to bacterial growth, the effete pro- 

 ducts of this on proteids belonging to the aromatic series of organic 

 compounds (phenol, kresol, indol and skatol, see p. 238). 



The portion containing thymol is boiled and filtered, and the 

 filtrate then evaporated to small bulk. A sample of the resulting 

 syrup is placed in a watch-glass, and allowed to stand exposed to the 

 air for a day or so. Then examine a drop on a microscopic slide, 

 and note the crystals of Leucin and Tyrosin. 



Leucin and Tyrosin. During digestion of hemi-peptone by trypsin a 

 number of amido acids are produced, of which leucin and tyrosin are 



1 There is, however, no primary proteose formed by tryptic digestion ; there is, 

 however, a considerable amount of secondary proteose (see p. 449). 



2 These digests are prepared beforehand by the demonstrator. 



