This section is from the book "Practical Cooking And Serving", by Janet McKenzie Hill. Also available from Amazon: Practical Cooking and Serving: A Complete Manual of How to Select, Prepare, and Serve Food [1919].

This dish when properly prepared is a delicate, dainty morsel. An egg so cooked is often more easily digested than when poached au naturel, in as much as the air incorporated into the white separates the cells of albumen and enables the digestive fluids to penetrate the mass without hindrance. (For recipe, see "Poached Egg Hygienic Fashion.") An egg thus cooked, and served in a tumbler, presents an attractive appearance most desirable in the sick room. The lower part of a small double-boiler, in which a trivet is set, affords a practical means of cooking. In the absence of a trivet one may be improvised by driving a nail repeatedly through the cover of a pound size baking-powder box. Thus the water may pass beneath the glass. Set the glass in place, while the water is lukewarm, and, when the white begins to expand with the heat and rise, drop in the yolk; both are cooked, at least, as soon as the water boils. The less the egg is cooked the more easily it will be digested.
 
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