35 



151. Fill a test-tube one-third full of milk, add some ren- 

 net. Keep in the water bath at 40° C. for a few minutes and 

 note the changes that occur. 



152. Dilute 5 cc. of milk with 15 cc. of water, add a little 

 dilute acetic acid and warm. A precipitate is formed. Fil- 

 ter and save both precipitate and filtrate. This precipitate 

 is not the same as that obtained by rennet. The acid pre- 

 cipitate is caseinogen, and is freely soluble in dilute alkali, 

 the rennet clot is " casein," and is much less soluble in di- 

 lute alkali. Cheese is made with rennet and cannot be made 

 with acid. 



153. The filtrate obtained from 152 is to be divided into 

 two portions. To the first portion apply Trommer's test. 

 A red precipitate indicates the presence of a reducing sugar 

 — lactose. 



154. To the second portion of the filtrate apply the xan- 

 thoproteic reaction. An orange color represents the pres- 

 ence of a proteid (lact-albumin). 



155. To the precipitate obtained from 152 add a little 

 ether in a test-tube and agitate for a few minutes. Pour off 

 the ether upon some paper and note that it leaves a perma- 

 nent greasy stain indicating the presence of fat. 



156. To the residue left in 155 add a little dilute caustic 

 potash (^o.ifo). A solution is effected. Apply the xan- 

 thoproteic reaction to this fluid. An orange color denotes 

 the presence of a proteid — caseinogen. 



157. To a test-tube half filled with 0.2% hydrochloric 

 acid and 15 drops of gastric extract add a small piece of 

 cheese. Put the tube in the incubator and examine at the 

 next exercise for peptones and intermediate products. 



158. The action of milk with pancreatic extract is some- 

 what complicated on account of the complexity of milk 

 itself. The sugar, fat and proteids all undergo some change 

 from the action of the different pancreatic ferments. Per- 

 haps the most interesting of these changes is that produced 



