There are two types of camels: Bactrian, which have only one hump but are strong; and Arabian, which have two humps and are more numerous. They hate horses. Camels can endure thirst for three days and prefer to drink muddy water; if only clear water is available, they will stir it up with their feet to muddy it. When they drink, they fill up for both past thirst and for future needs. Some camels are good for carrying burdens, while others are better suited to travelling. Their hoofs do not wear down. They can live for one hundred years, unless they are taken to a foreign country, where the change of air makes them ill. Female camels are used in war. Camels grow wild with the desire to mate; this desire can be destroyed by castration, which also makes the camel stronger.