The value of the slave as an economic machine depended upon his physique, health and general endurance. The slave hunters were Portuguese, Spaniards and Arabs, who drove the negroes in gangs down to the coast, where they were loaded upon the slave ships. When the trade was brisk and prices high, the hold of the ship was crowded to suffocation, and intense suffering was inevitable. Landing at Savannah or Charleston, Mobile or New Orleans, the slaves were sold at wholesale, in the auction place. Later, the slave dealer drove them in gangs through the villages, where they were sold at retail. The cost of a slave varied with the price of cotton. Of the three million one hundred thousand slaves living in the South in 1850, one million eight hundred thousand were raising cotton. That was the great export, the basis of prosperity. So great was the demand in England for Southern cotton that profits were enormous. The Secretary of the Treasury in Buchanan's time published a list of forty Southern planters in Louisiana and Mississippi. One of them had five hundred negroes and sold the cotton from his plantation at a net profit of one hundred thousand dollars. Each negro, therefore, netted his master that year five hundred dollars. The working life of a slave was short, scarcely more than seven years, and for that reason the ablest negro was never worth more than from a thousand to twelve hundred dollars. But if the cost of free labour was high, the cost of supporting the slave under the Southern climate was very low. The climate of the Gulf States is gentle, soft and propitious. Of forty planters who published their statements, the average cost of clothing and feeding a slave for one year was thirty dollars. One Louisiana planter, however, showed that one hundred slaves on his plantation had cost him in cash outlay seven hundred and fifty dollars for the entire year. This planter states that his slaves raised their own corn, converted it into meal and bread, raised their own sugar-cane, made their own molasses, built their own houses out of the forest hard by. The slaves also raised their own bacon, but unfortunately the price of meat was so high as to make its use only an occasional luxury. North Carolina passed a law commanding the planters to give their slaves meat at certain intervals, but the law remained a dead letter. Other states, by legal enactment, fixed the amount of meal that should be given to slaves.