In judging of the welfare of the slaves, it is necessary to distinguish the different conditions of slavery. The most important distinction, both as regards numbers and its influence on the well­being of the slave, is that between house­servants and farm or field­hands. The house­servant is comparatively well off. He is frequently born and bred in the family he belongs to. The position of the field­hands is very different; of those, especially, who labour on large plantations. Here there are none of those humanizing influences at work which temper the rigour of the system, nor is there the same check of public opinion to control abuse. The 'force' is worked as a great human mechanism; as a drove of human cattle. --James Stirling, 1857 What is the MAIN idea of the author's description of life on a southern plantation?