We hardly know how useful it really is until we are deprived of some of our other senses, as sight or hearing.

In a blind man the sense of touch often becomes surprisingly acute.
~31.

Effects of Alcohol and Tobacco on the Special Senses.~--All the special senses--hearing, seeing, smelling, tasting, feeling--depend upon the brain and nerves.

Whatever does harm to the brain and nerves must injure the special senses also.

We have learned how alcohol and tobacco, and all other narcotics and stimulants, injure and sometimes destroy the brain cells and their nerve branches, and so we can understand that a person who uses these poisonous substances will, by so doing, injure the delicate organs with which he hears, sees, smells, etc.
~32.~ Persons who use tobacco and strong drink sometimes become blind, because these poisons injure the nerves of sight.