Tell them how the cheesemaker separates sweet milk into curd and whey.
If advisable, let them do it, but in any case show them some sweet milk separated by rennet. Examine the sweet whey. It tastes sweet, denoting the presence of _sugar_--another carbonaceous food.
Notice the greenish-yellow colour. Recall this same colour in water in which potatoes, cabbage, or other vegetables have been cooked. Tell the pupils that this colour is given by _mineral matter_ being dissolved in the water.
There is still the curd of milk to examine. The use of the senses does not allow us to definitely decide what food substance the curd is. Tell the pupils it is protein, or find the name by a process of reasoning, thus: Recall the fact that babies live for several months on milk alone and during that time build all tissues of the body. Milk, therefore, must contain all tissue-building substances. Review the food substances which are necessary to build all body tissues--mineral matter, protein, and water. We have found the mineral matter and water in milk, but not the protein. Since curd is the only remaining part of milk, it must be largely protein.
Tell the pupils that the scum which comes on the top of milk, when it is boiled, is another kind of protein of which there is a small amount in solution in milk.
Lead the pupils to see that if starch were present, it would be in a raw form, and in this form is indigestible.
LESSON II
FOOD VALUE
The analysis of milk gives a key to the food value of milk and each of its by-products (cream, butter, butter-milk, sour milk, skim milk, curd, whey, cheese, junket). These may now be briefly discussed as to composition, food value, and cost.
CARE
Milk readily absorbs odours, bacteria, etc., and should be kept in covered, sterilized dishes in a pure, cool atmosphere.
EFFECT OF HEAT
Experiments should be made to show the effect of simmering and boiling temperatures. To save time, a different experiment may be given to each pupil, and the results reported.
1. Simmer sweet milk and note the flavour.
2. Boil sweet milk and note the flavour.
3. Simmer the curd of milk. Examine its texture.
4. Boil the curd of milk. Examine its texture and compare it with the simmered curd.
5. Boil skim milk and note the scum.
6. Simmer skim milk and note the absence of scum.
NOTE.--From the above experiments deduce the effect of heat on protein.
Practice lessons may now be given in preparing simple dishes in which milk is the main ingredient, or, at least, recipes may be given for these to be made at home. The following would be suitable: cream sauce, cream soups, custard, junket, cottage cheese, albuminized milk.
STUDY OF EGGS
LESSON I
PARTS
(1) Shell, (2) thick membrane, (3) white, (4) thin membrane, (5) yolk.
These parts are easily seen. Attention should be called to the pores in the shell, and it should be explained that these allow the entrance of bacteria which spoil the egg. Any means of closing these pores helps to preserve the egg.
METHODS OF PRESERVING
Cover the holes in the shell as follows:
1. Pack in salt, bran, sawdust, brine, or water-glass.
2. Coat the shells with fat or wax.
3. Wrap the eggs in paper.
[Illustration: Testing eggs by floating: (1) slightly stale, (2) stale, (3) very stale]
TESTS
1. In the shell:
After an egg is laid, the liquid which it contains begins to evaporate through the pores of the shell and, as this continues, a noticeable space is left inside.
(1) Shake the egg, holding it near the ear. If the contents rattle, it is somewhat stale.
(2) Drop the egg in cold water. If it sinks, it is fresh.
(3) Hold the egg between your eye and the light. If clear, it is fresh.
(4) A rough appearance of the shell denotes freshness.
2. Out of the shell:
White--this should be clear and cling to the yolk.
Yolk--this should round up like a ball.
CARE
1. If eggs are to be used in the near future, they should be washed and put in a pure, cool atmosphere. The lower shelf of the refrigerator is best, as odours rise, and eggs readily absorb these.
2. If eggs are to be preserved, they should not be washed unless their condition compels it, as washing removes the natural covering of the pores. They should be stored in a clean, cool place, and packed as soon as possible.
LESSON II
COMPOSITION