The insolubility of starch in cold liquids may be effectively reviewed at this part of the lesson. The starch has been lying in the water of the potato cells for several months, yet has not dissolved. Let two or three of the class gradually heat the potato juice with its starch sediment, stirring all the time to distribute the sediment evenly. They will find that a little less than boiling temperature dissolves the starch. This will show them that heat is necessary for the solution of starch, and a heat much greater than that in the body, hence raw starch is indigestible. Recall the milk lesson and the uselessness of starch as a component of milk, unless the milk be cooked.
Squeeze the juice from a sour apple or lemon, and note the taste. Explain that all fruit juices contain more or less acid. The effects of this acid in the body are similar to those of mineral matter.
Protein is also found in plant juices; but in such small quantities that it may be disregarded as a source of food supply.
GENERAL COMPOSITION OF PLANT JUICE
Water; mineral matter; flavouring matter; starch or sugar, or both; acid (in fruit juice).
Lesson III
COMPOSITION OF SOLID MATERIAL IN CELLS OF SEEDS
This part of the lesson may be developed as follows:
1. Seeds contain the building material for new plants, as well as their food for a short time.
2. Plants and animals require much the same material to build and feed them.