Several hundred years ago the Sultans of Zanzibar grew powerful and wealthy through exporting slaves and ivory from the mainland.  These were not two separate industries, but one was developed by the other and was dependent upon it.  The procedure was brutally simple.  A slave-trader, having first paid his tribute to the Sultan, crossed to the mainland, and marching into the interior made his bargain with one of the local chiefs for so much ivory, and for so many men to carry it down to the coast.  Without some such means of transport there could have been no bargain, so the chief who was anxious to sell would select a village which had not paid him the taxes due him, and bid the trader help himself to what men he found there.  Then would follow a hideous night attack, a massacre of women and children, and the taking prisoners of all able-bodied males.  These men, chained together in long lines, and each bearing a heavy tooth of ivory upon his shoulder, would be whipped down to the coast.  It was only when they had carried the ivory there, and their work was finished, that the idea presented itself of selling them as well as the ivory.  Later, these bearers became of equal value with the ivory, and the raiding of native villages and the capture of men and women to be sold into slavery developed into a great industry.  The industry continues fitfully to-day, but it is carried on under great difficulties, and at a risk of heavy punishments.  What is called “domestic slavery” is recognized on the island of Zanzibar, the vast clove plantations which lie back of the port employing many hundreds of these domestic slaves.  It is not to free these from their slight bondage that the efforts of those who are trying to suppress the slave-trade is to-day directed, but to prevent others from being added to their number.  What slave-trading there is at present is by Arabs and Indians.  They convey the slaves in dhows from the mainland to Madagascar, Arabia, or southern Persia, and to the Island of Pemba, which lies north of Zanzibar, and only fifteen miles from the mainland.  If a slave can be brought this short distance in safety he can be sold for five hundred dollars; on the mainland he is not worth more than fifteen dollars.  The channels, and the mouths of rivers, and the little bays opening from the Island of Pemba are patrolled more or less regularly by British gunboats, and junior officers in charge of a cutter and a crew of half a dozen men, are detached from these for a few months at a time on “boat service.”  It seems to be an unprofitable pursuit, for one officer told me that during his month of boat service he had boarded and searched three hundred dhows, which is an average of ten a day, and found slaves on only one of them.  But as, on this occasion, he rescued four slaves, and the slavers, moreover, showed fight, and wounded him and two of his boat’s crew, he was more than satisfied.