insisted that they should come with empty stomachs, and then sent them home as hungry as wolves. About this time he also succeeded in demonstrating that frogs exhale more carbonic acid in the light than in the dark, thus proving that light accelerates the processes of assimilation in animal organisms, and that, too, independently of the temperature of the environment or the motion of the animal.
Meanwhile he had prepared and published his Lehre der Nahrungsmittel (Erlangen: Enke, 1850). This work, of less than two hundred and fifty pages, written "für das Volk," and admirably adapted to convey popular information concerning the digestive qualities and nutritive properties of common articles of food, was favorably received, and in a few years passed through three editions. It presented in a clear and concise manner the results of researches embodied in his Physiologie der Nahrungsmittel, issued a few months earlier and intended for physicians and naturalists, and was translated into Dutch, English, French, Italian, Spanish, and Russian. It is divided into three principal parts, the first of which treats of the general metamorphosis of matter in living organisms, the origin and formation of the blood and of the solids in the human body, the processes of assimilation, segregation, and excretion as the conditions of growth, and the physiological nature of hunger and thirst as sensations which inform the brain through the medium of the nerves that the blood is being impoverished. In the second part he shows how this impoverishment is checked and the waste repaired by nutriment, of which the various kinds—meat, eggs, bread, cake, peas, beans, lentils, potatoes, beets, cabbage, and other vegetables, and different sorts of fruit—are discussed as to their alimentary functions and value. We then have a chapter on drinks—water, milk, tea, coffee, chocolate, beer, wine, and brandy—and another on spices, or rather on condiments, in which are included not only salt, pepper, mustard, ginger, and other spices, but also butter, olive oil, vinegar, sugar, and cheese. In the third part there are rules of diet in their application to man as a not strictly omnivorous, but largely multivorous microcosm, with remarks on breakfast, dinner, and supper, nutriment for infancy, youth, middle life, and old age, for women, workmen, artists, scholars, and other persons of sedentary habits, and the different sorts of food suitable for summer and winter. All these points are discussed in a series of short sections with a perspicacity and perspicuity and power of condensation rarely combined in scientific treatises. This feature of the work was especially praised by Alexander von Humboldt.
Perhaps even a greater sensation than by the book itself was made by a long review of it in a Leipsic weekly journal (Blätter für literarische Unterhaltung, November 9, 1850), by Ludwig
