MILK. 295 



At the present time the digestion, or peptonization of milk, is a very 

 common practice in the preparation of food for the sick room, and can be 

 illustrated by the following experiment: 



Ex. Dilute about 10 cc. of milk with an equal volume of water, and add 

 half a gram of sodium bicarbonate. Next add a few drops of a liquid ex- 

 tract of pancreas, or a very small amount (10 to 20 mg.) of one of the 

 concentrated "pancreatin" powders on the market. Shake the mixture 

 and keep it at a temperature of 40 degrees on the water-bath half an hour. 

 At the end of this time filter and apply the peptone test potassium hy- 

 droxide and dilute copper sulphate and observe the pink color. As the 

 action of the pancreatic extract is continued the liquid resulting becomes 

 very bitter from the formation of digestion products other than "peptone." 

 The reaction should therefore be checked by cooling before this very bitter 

 stage is reached. 



It will be observed that these experiments illustrate the con- 

 ditions in two kinds of digestion. The pancreatic digestion 

 of proteins in milk is favored by a neutral or slightly alkaline 

 reaction. Alkali interferes with the rennet coagulation. In 

 the stomach the clotting of the milk is favored by the combined 

 action of the acid and ferment. In the normal stomach coag- 

 ulation the presence of calcium salts seems to be essential. If 

 milk be treated with a small amount of sodium oxalate solution 

 and then rennet, coagulation fails. Calcium chloride solution 

 added later, the proper temperature being meanwhile main- 

 tained, brings it about. 



THE ANALYSIS OF MILK. 



The above experiments suggest some of the steps in the 

 quantitative analysis of milk, a brief outline of which follows : 



Water and Total Solids. Weigh out about 5 grams in a small platinum 

 dish and evaporate to dryness over a water-bath which requires some 

 hours. Then transfer the dish to a hot air oven and maintain at a 

 temperature of 105 through half an hour. Cool the dish in a desiccator 

 and weigh. The loss of weight represents the water, as practically nothing 

 else of consequence is volatile. 



Ash or Mineral Matter. After weighing the dry residue or total solids 

 above place the dish on a triangle over a clear Bunsen flame and heat 

 until all the organic matter and finally the excess of carbon is driven off. 

 The ash left must be perfectly white. Cool and weigh as before. There 

 is some slight loss of volatile salts in this ignition. 



Fat. Where many analyses are made as a routine operation, as in the 



