XVIII. (105) The animals which are clean and lawful to be used as food are ten in number; the heifer, the lamb, the goat, the stag, the antelope, the buffalo, the roebuck, the pygarga, the wildox, and the chamois, {19}{#de 14:4.} for he always adheres to that arithmetical subtilty which, as he originally devised it with the minutest accuracy possible, he extends to all existing things, so that he establishes no ordinances, whether important or unimportant, without taking and as it were adapting this number to it as closely connected with the regulations which he is ordaining. Now of all the numbers beginning from the unit, the most perfect is the number ten, and as Moses says, it is the most sacred of all and a holy number, and by it he now limits the races of animals that are clean, wishing to assign the use of them to all those who partake of the constitution which he is establishing. (106) And he gives two tests and criteria of the ten animals thus Enumerated{20}{#le 11:3.} by two signs, first, that they must part the hoof, secondly, that they must chew the cud; for those which do neither, or only one of these things, are unclean. And these signs are both of them symbols of instruction and of the most scientific learning, by which the better is separated from the worse, so that all confusion between them is prevented; (107) for as the animal which chews the cud, while it is masticating its food draws it down its throat, and then by slow degrees kneads and softens it, and then after this process again sends it down into the belly, in the same manner the man who is being instructed, having received the doctrines and speculations of wisdom in at his ears from his instructor, derives a considerable amount of learning from him, but still is not able to hold it firmly and to embrace it all at once, until he has resolved over in his mind everything which he has heard by the continued exercise of his memory (and this exercise of memory is the cement which connects ideas), and then he impresses the image of it all firmly on his soul. (108) But as it seems the firm conception of such ideas is of no advantage to him unless he is able to discriminate between and to distinguish which of contrary things it is right to choose and which to avoid, of which the parting of the hoof is the symbol; since the course of life is twofold, the one road leading to wickedness and the other to virtue, and since we ought to renounce the one and never to forsake the other.