COMMENTARY. The remarks of our author on the effects of exercise are exceedingly pertinent and comprehensive. See, in like manner, Aëtius (iii, 2), and Oribasius (Med. Collect. vi, 11.) But Galen is the great authority on this subject, which he treats of very fully and philosophically, in the second book of his ‘Hygiene.’ He agrees entirely with Hippocrates, that the proper time for exercise is before a meal, because, the excrementitious superfluities being thereby evacuated, the body is in a fit condition for receiving a new supply. He explains, however, afterwards, that it is after the digestion and distribution of a preceding meal have been accomplished that exercise will be most proper. According to Haly Abbas, exercise is useful for three purposes: 1. For rousing the innate or natural heat, whereby the processes of digestion and distribution are accelerated. 2. For opening the pores of the body, and evacuating its superfluities. 3. For strengthening and rousing the animal actions, by the friction it occasions. (Theor. v, 2.) Avicenna gives nearly the same statement of the good effects of exercise. Haly Abbas forbids exercise immediately after dinner. He adds, that exercise taken immediately after a meal makes the food descend to the intestines, where it is absorbed by the veins before it is properly concocted, and thereby the liver becomes loaded with crudities. (Pract. i, 3.) Alsaharavius recommends exercise before a meal, but advises it not to be continued after one feels fatigued and languid. (Theor. ii, 2.) The same rule is distinctly laid down by Rhases. (Contin. xxxiii.) It appears that, instead of taking exercise after food, the ancients were in the practice of indulging in a short sleep after their dinner or mid-day meal. See Plautus (Mostell. ac. iii, sc. 2, 1. 8), and the note of Meursius (Ed. Gronov.) Homer says that it is beneficial to old men to indulge in sleep after the bath and taking food. (Galen. Hyg. 1.) Plutarch mentions that Cicero was cured of debility of the stomach by taking moderate exercises. (In vita Cicer.) It was one of the extravagant opinions of Erasistratus, that exercise is not at all necessary for the health of the animal frame. SECT. XVII.—ON THE KINDS OF EXERCISE.