RENNIN. 79 



189. In order to purify rennin, precipitate it with basic 

 lead acetate and filter. Wash the precipitate, then suspend it 

 in water, and acidify slightly with sulphuric acid. Filter, and to 

 the filtrate, which contains the rennin, add a solution of stearin 

 soap. The latter is decomposed by the acid, stearic acid being set 

 free as an insoluble precipitate. This carries the rennin with it. 

 Filter and place the precipitate, with a small amount of water, in 

 a glass-stoppered funnel. Add ether, shake, and after the ether 

 has separated above the watery solution draw off the latter. The 

 fatty acids from the decomposed soap have remained in the ether, 

 leaving the rennin dissolved in the water. 



190. Test the solution or a specimen of normal or 

 artificial gastric juice for rennin by exactly neutralizing, 

 then adding it to an equal volume of milk in a test-tube. 

 Place the tube in a beaker of water at body-temperature. 

 If rennin is present the casein will be coagulated in twenty 

 or thirty minutes. 



A solution of casein may be used instead of milk, but 

 in order to make it coagulate a small amount of a calcium 

 salt must be added. 



For demonstrating the properties of rennin the com- 

 mercial product, which is sometimes sold under the name 

 of junket, may be employed. 



191. To 5 cubic centimeters of milk add 1 cubic 

 centimeter of rennin solution and keep at body-tempera- 

 ture. Note the time of coagulating. 



192.- Eepeat the above, adding 2 cubic centimeters 

 of ammonium oxalate solution to the mixture of milk and 

 rennin. This precipitates calcium from its solutions. 

 How does it influence coagulation ? Will it now coagulate 

 if calcium chlorid is added ? 



193. Is the rennin, after it has been boiled, capable 

 of coagulating milk? What does this show as to its 

 nature ? 



