13. Who does not see the necessity that the evil should be separated from the good, lest the latter should be infected with the contagion of deadly evil, and perish? For evil, inasmuch as it is implanted in human nature by birth, and more and more ingenerated in children from parents when the Church is approaching consummation, is like the malignant disease which is called cancer, which spreads round about, and gradually mortifies the healthy and living parts. What husbandman, or gardener, when he sees briars, nettles, thorns and thistles growing, does not extirpate them before he sows and tills his corn and food crops? What farmer, when be sees his young crops and grass consumed by worms, or locusts, does not dig a ditch, and separate the flourishing field from the wasted one, and thus take measures for the preservation of his crops and thriving fields? What shepherd, when he sees wild beasts multiplying about his sheep pastures, does not call together the neighbouring shepherds and the servants, and with weapons, or traps, kill those wild beasts, or drive them away? [2] What king, when he sees both the towns of his kingdom round about his metropolis taken by enemies, and the property of his subjects seized by them, does not assemble the troops and cast out the enemy, and restore the stolen goods to their owners, and, moreover, add thereto the spoils of the enemies' wealth, and so compensate them?