Speaking generally, slavery exists now only in Mohammedan countries (though there are a few exceptions), yet it cannot be called a Mohammedan institution. The Prophet sanctioned only the taking of slaves in war. The custom of his time was to kill and often to torture prisoners taken in war, so that really it was a step in advance to suggest that these captives should be utilised as servants. To a great extent, if not entirely, slavery as an institution is due to the low moral standard set up by the Koran. Were it not for love of sensual indulgence, slavery would long ago have died a natural death. Over and over again has it been proved that voluntary service is far cheaper than enforced labour. An Indian coolie will work all day, and ask for little more than enough to keep body and soul together. This much the slave-owners are compelled to give to keep their slaves in health. Slaves are valuable property, and it is cheaper to feed them well than badly. But over and above the food, the slave-owner has to bear the cost of transit from their bright happy homes in Central Africa, through hundreds of miles of scorching desert, which demands a frightful death-toll. Only the strongest ever reach the slave-markets, and it has been calculated that at least 500,000 lives are annually sacrificed during transit. Indirectly the slave-owner has to pay for these. When slaves were taken in war, they cost nothing to transport; but when Mohammedan conquests ceased, the supply ceased with it, for Mohammedans are not allowed by the Koran to make slaves of men of their own creed, though they do sometimes infringe this rule.