9. When females are urged with desire, their genital organs are swollen with heat, and a fluid secretion takes place. Mares scatter about a white fluid at this season. In no creatures are the catamenia so abundant as in women. In sheep and goats at the season of coition, there are certain signs before copulation: there are also signs after copulation, but these again cease till the period of parturition, when they again occur. By this means shepherds understand that they are about to produce their young. After parturition there is a great purification, which at first is not very full of blood, but becomes so afterwards. 10. In the cow, the ass, and mare, this purification is abundant, on account of their great size; but still it is small, considering how large they are. When the cow is urged by desire, she undergoes a brief purification, about half-a-cup full, or a little more. The time of this purification is peculiarly the period for sexual intercourse. Of all quadrupeds the mare suffers the least, and is the most cleanly in parturition: neither is her loss of blood great considering the size of the animal. In cows and mares, the failure of the catamenia in the second, fourth, and sixth month is considered as a sign of pregnancy; but it is not easy for anyone to understand this, who does not follow and accustom himself to them: and some persons are of opinion that they have no catamenia. The female oreus has no catamenia, but her urine is thicker than that of the male. 11. On the whole, the liquid excrements are thicker in other animals than in man; and those of female sheep and goats thicker than in the males of the same animal. That of the she ass is thinner, of the cow is harsher, than of their respective males. After parturition the urine of all creatures becomes thicker, and especially in those which have no purification. When females begin to feel sexual desires, their milk is like pus; it afterwards becomes useful after parturition. Sheep and goats become fat when they are pregnant, and consume more food; and so do cows, and all other quadrupeds. CHAPTER XVIII. 1. Generally speaking, the sexual desires of animals are more violent in spring. They do not all, however, copulate at the same seasons, but at the time of year which will cause them to produce their young at the proper season. The period of gestation in domestic swine is four months. They never produce more than twenty pigs; and if they have many, they cannot bring them all up. When aged, they produce in the same manner, but they copulate more slowly. They become pregnant with one act of coition; but they submit themselves to the boar very frequently, on account of their rejection of the capria after they are pregnant. This takes place in all, but some will also eject the semen.