ELEMENTARY CHEMICAL PHYSIOLOGY 233 



all put about 5 c.c. milk, then to (a) add 5-10 drops of a solution 

 of rennin, to (6) 5-10 drops rennin which has previously been 

 boiled, to (c) 5-10 drops rennin + 5 drops 0-2 per cent, potassium 

 oxalate solution, to (d) 5-10 drops rennin + 5 drops 0-2 per cent, 

 potassium oxalate solution -j- 3^4 drops 5 per cent, calcium chloride 

 solution, and to (e) 5-10 drops rennin -f 5 drops 0-2 per cent, 

 potassium oxalate solution, after standing ten minutes heat to 

 boiling, cool and add calcium chloride solution. Shake test tubes 

 a, 6, c, d well and place in a water bath at 40 C. for five to ten 

 minutes. Tube e treat as directed. 



Tube (a) clots, (6) no clotting, (c) no clotting, (d) clots, (e) clots. 

 Rennin and calcium salts are therefore necessary for the curdling 

 of milk. Further, although rennin alone cannot clot milk, yet as 

 test tube e shows it produces some change in the caseinogen which 

 is completed by the addition of a calcium salt (see Milk, p. 328). 



CHAPTER IX 

 DIGESTION IN THE INTESTINE 



Pancreatic Digestion. In studying the digestive action of this 

 juice we may employ, as in the case of gastric digestion, an extract 

 of the gland. This extract may be made with glycerine, or prefer- 

 ably water, after activation of the zymogens present in the minced 

 tissue by means of the addition of a small amount of intestinal 

 mucosa scrapings. 



There are three active ferments in pancreatic juice, one proteo- 

 lytic -trypsin ; one amylolytic amylopsin or diastase ; one 

 lipolytic steapsin or lipase. 



Trypsin. Like pepsin, this ferment hydrolyses protein, and leads 

 to the production of proteoses and peptones. In this case, however, 

 digestion is more complete. Under suitable conditions the proteoses 

 and peptones can disappear entirely, polypeptides and amino acids 

 resulting ; the ultimate decomposition products are, in fact, almost 

 the same as when a strong acid is used as the hydrolysing agent 

 (see Proteins, p. 193). 



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

 sodium carbonate is prepared (Liq. Pancreaticus (Benger), diluted 

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

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

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

 solution, and place in 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 dis- 

 appeared remove a sample of the digest, and neutralise with weak 



