This section is from the book "Mrs. Rorer's Vegetable Cookery And Meat Substitutes", by Sarah Tyson Rorer. Also available from Amazon: Mrs. Rorer's Vegetable Cookery And Meat Substitutes.......
Vegetables are divided into four groups. The first group is the muscle-making, or nitrogenous. These have meat value and take the place of meat. Old peas, beans, lentils and nuts are the chief in this group. Mushrooms contain nitrogen but in no way take the place of meat.
Such manufactured foods as macaroni, spaghetti and the cereals also contain nitrogen mixed with a goodly quantity of starch, for which reason they are placed in the carbohydrate group.
The second group - the carbohydrate - are heat-and energy-producers, hence must be used in larger quantites than the muscle-building foods - meat substitutes. In this second group we have rice, sweet and white potatoes, white bread, chestnuts, macaroni and spaghetti and the cereals.
In the third or fatty group we have only certain nuts and olives.
The last group, by far the largest of the four, contains the green, succulent vegetables, largely water, some mineral matter, and a great deal of flavoring material. They are important as cleansers. They keep up the peristaltic action of the intestines. These foods are also called waste or bulk foods and are to my mind just as necessary to the balanced ration as the first three groups.
Olive oil and nut fats take the place of cream and butter and may be substituted in all the following recipes for butter without change of quantity.
All vegetables not containing starch - lettuce, chicory, cabbage and celery - may be eaten raw. Beets, carrots and turnips do not contain starch. Eaten raw they are dense and indigestible unless thoroughly masticated or grated.
All vegetables should be put over the fire to cook in rapidly boiling water, and in uncovered vessels.
Top-ground, succulent or green vegetables should be cooked in salted boiling water.
Underground vegetables, the roots and stems of plants, should be cooked in boiling unsalted water. Salt should be added after they have been drained.
Old peas, beans and lentils should be washed and soaked over night. In the morning drain, cover with fresh boiling water, boil half an hour, drain, and throw this water out. They are now ready to cook according to any of the various recipes. This first treatment makes them more delicate and wholesome.
Vegetables containing starch - rice, potatoes, chestnuts - must be boiled until tender but not a moment longer or they will become heavy and soggy.
Many nitrogenous vegetables contain vegetable casein and cannot be easily cooked in hard or limestone water.
If vegetables are wilted, soak them in clear, cold water before cooking. Under no circumstances add salt to the water as it draws out the juices, hardens the fibre and destroys the flavor.