passages, where they arrive in too large a number, or are of irregular figures, or move too fast or proceed too slow: that phrensies, lethargies, pleurisies, burning fevers, for example, are occasioned by these corpuscles stopping of their own accord: that pain is produced by the stagnation of the largest of all these corpuscles, of which the blood consists: that, on the contrary, deliriums, languors, extenuations, leanness and dropsies derive their origin from a bad state of the pores, which are too much relaxed, or opened: that dropsy, in particular, proceeds from the flesh being perforated with various small holes which convert the nourishment received into them into water; that hunger is occasioned by an opening of the large pores of the stomach and belly: that thirst arises from an opening of the small pores: that intermittent fevers have the same origin: that quotidian fever is produced by a retention of the largest corpuscles; tertian fever by a retention of corpuscles somewhat smaller; and quartan fever by a retention of the smallest corpuscles of all. Galen maintained that the animal body is composed of three principles, namely, the solids, the humours, and the spirits: that the solid parts consist of similar and organic: that the humours are four in number, namely, the blood, the phlegm, the yellow bile, and the black bile: that the spirits are of three kinds, namely, the vital, the animal, and the natural; that the vital spirit is a subtle vapour which arises from the blood, and which derives its origin from the liver, the organ of sanguification: that the spirits, thus formed, are conveyed to the heart, where, in conjunction with the air drawn into the lungs by respiration, they become the matter of the second species, namely, of the vital spirits; that in their turn the vital spirits are changed into the animal in the brain, and so on.