The training of the senses
There are six senses which minister to knowledge: sight, hearing, smell, touch and taste, mind, and all of these except the last look outward and gather the material of thought from outside through the physical nerves and their end-organs: eye, ear, nose, skin, palate. The perfection of the senses must be one of the first cares of the teacher. Two things that are needed of the senses are accuracy and sensitiveness. We must first understand what are the obstacles to the accuracy and
sensitiveness of the senses, in order that we may take the best steps to remove them. The senses depend for their accuracy and sensitiveness on the unobstructed activity of the nerves which are channels of their information and the passive acceptance of the mind which is the recipient. The fault may be with the nerve currents. The nerves are nothing but channels. They have no power in themselves to alter the information given by the organs. But a channel may be obstructed and obstruction may interfere either with the fullness or the accuracy of the information as it reaches the mind. … The obstructions can be removed and the sensitiveness remedied by the purification of the nervous system. The remedy is a simple one: the regulation of the breathing. This process is called in Yogic discipline nādi-śuddhi or nerve purification. All distortion due to actions in the nervous system can be traced to some kind of emotional disturbance acting in the nerve channels. The only remedy for them is the habit of calm, the habitual steadiness of the nerves. This also can be brought about by nādi-śuddhi or nerve purification. Now the manas, the mind, or sixth sense is in itself a channel like the nerves, a channel for communication with the buddhi or brain-force; the manas is both a sense organ and a channel.