614 IOWA DEPARTMENT OF AGRICULTURE 



strained while warm. It may therefore he in place here to suggest that 

 after sour milk has been scalded for the purpose of making cottage cheese 

 it is well to chill it thoroughly before straining. Through very common 

 processes, those of butter and cheese making, one may become familiar 

 with the solid known as casein and with the fat of milk. But the clear 

 whey which may be separated from the curd also has important solids in 

 it and with these one seldom has a chance to become acquainted. The fol- 

 lowing simple experiment may be carried out with the ordinary dishes 

 in use in the kitchen: 



Separate a portion of whey from the curd of sour milk, and, if neces- 

 sary to make it perfectly clear, strain through a piece of fine cloth without 

 previously heating. Examine to see that there are no solid particles 

 in it. Divide into two parts. Heat one part to the boiling point, and 

 when cool pour into a glass, examine, and compare with the unheated 

 portion. The part that has been heated will be seen to be full of small 

 particles of a white solid which soon sink to the bottom of the liquid. 

 This is albumen, a substance always present in cows milk, though in 

 very much smaller amount than the casein. It resembles the albumen 

 of the white of an egg. It differs from the casein in not curding when 

 the milk sours and in remaining in solution in the whey. Furthermore, 

 it does not form curd in the stomach. This experiment is particularly 

 important to those who wish to understand milk in its relation to the 

 feeding of babies. The proteid which by the process of heating is shown 

 to be present in the whey is the chief proteid of human milk, while in 

 cows milk, as has been said, it is found in very much smaller amount 

 than the curding proteid. Cows milk, therefore, can never be a perfect 

 equivalent for human milk in infant feeding, even if diluted and modi- 

 fied, though it may be the best available substitute for it. It is easy to 

 understand that a baby may be able to digest a proteid which remains 

 dissolved in the whey more easily than one which curds soon after 

 reaching the stomach. 



To continue the experiment with milk, strain the whey which has 

 been heated and again get a clear liquid. Pour this into a double boiler 

 over water and heat until it is dry. There will be left a solid sugary 

 mass. Place some of this in an old spoon or on a piece of tin or sheet iron 

 and burn. Notice the characeristic odor of charred sugar. Milk con- 

 tains 5 per cent of sugar. This sugar is not exactly like the sugar used 

 on the table. It is much less sweet and physiologists and chemists find 

 that it acts differently from ordinary sugar during the process of diges- 

 tion. For this reason the sugar used in preparing a baby's food should 

 never be granulated sugar, but milk sugar, which can be bought at 

 the druggist's. 



If it is possible to get the spoon in which the sugar is heated suffi- 

 ciently hot to burn the sugar completely, it will be discovered that there 

 remains behind a small portion of white powder, which the most intense 

 heat does not consume. This is the mineral matter of the milk. It con- 

 stitutes about seven-tenths of 1 per cent of its weight, and it is more 

 abundant in comparison with other nutrients than in any other common 



