Those actions of the body which they call natural, are inspiration and exspiration, the reception and concoction of our meat and drink, as also the distribution(5) of the same into the several parts of the body. They also inquire how it happens, that our arteries rise and fall; from what causes proceed sleep and watching; without the knowledge of which, they conceive it impossible for any person either to oppose the beginnings of diseases, that depend on these particulars, or cure them when formed. As of all these things they look upon concoction to be of the greatest importance, they insist chiefly upon it; and some of them following the opinion of Erasistratus, affirm that the food is concocted in the stomach by attrition; others, after Plistonicus, the disciple of Praxagoras, by putrefaction; others, upon the credit of Hippocrates, believe concoction is effected by heat. After them follow the disciples of Asclepiades, who hold all these hypotheses to be vain and idle; for that there is no concoction at all, but the matter, crude as it is received, is distributed through the whole body. And in these things they are by no means agreed: however, it is not disputed, that according to the different hypotheses, a different regimen of diet is to be observed by sick people. For if it be performed by attrition, such food is to be chosen, as will most easily be broken to pieces; if by putrefaction, such as most quickly undergoes that change; if heat be the cause of concoction, then such as most effectually cherishes heat. But if there be no concoction at all, then none of these kinds of aliment are to be chosen: but such are to be taken, as are least liable to change from the state in which they are received. And, by the same way of reasoning, when there is a difficulty of breathing, when sleep or watchings oppress, they are of opinion, that the man, who has first learned in what manner these happen, will be capable of curing them. Besides, as pains, and various other disorders, attack the internal parts, they believe no person can apply proper remedies to those parts, which he is ignorant of; and therefore, that it is necessary to dissect dead bodies, and examine their viscera and intestines; and that Herophilus and Erasistratus had taken far the best method _for attaining that knowledge_, who procured criminals out of prison, by royal permission, and dissecting them alive, contemplated, while they were even breathing, the parts, which nature had before concealed; considering their position, colour, figure, size, order, hardness, softness, smoothness, and asperity(6); also the processes and depressions of each, or what is inserted into, or received by another part; for, _say they_, when there happens any inward pain, a person cannot discover the seat of that pain, if he have not learned where every viscus or intestine is situated; nor can the part, which suffers, be cured by one, who does not know what part it is; and that