851. The nerves that supply the sense of touch, proceed from the anterior half of the spinal cord. Where this sense is most acute and delicate, we find the greatest number of sensitive nervous filaments, and those of the largest size. _Observation._ In amputating limbs, and other surgical operations, the division of the skin causes more pain than all the subsequent steps of the operation, however protracted. The muscles, cellular membrane, and fat have but little sensibility; while the bones, tendons, and ligaments are insensible when not diseased, and may be cut without causing pain. HYGIENE OF THE SENSE OF TOUCH. 852. The sense of touch varies in different persons, and also in individuals of different ages. Thus the sensibilities of the child are more acute than those of the aged. Although there is an original difference of sensibility from organization, still, the function of the nerves of sensation is modified by certain influences. 853. _The healthy or unhealthy, active or inactive state of the brain, influences the action of the sensitive nerves._ In sound and perfect sleep, the brain is inactive. In this state, ordinary impressions made upon the skin are not observed by the sleeping person. Thus the arm may be blistered while sleeping, when exposed to the warm rays of the sun, and the individual will not be aware of it at the time. -=-=-=-=-=-=-=-=-=-=-=-= 851. From what do the nerves proceed that supply this sense? 852-864. _Give the hygiene of the sense of touch._ 852. Does this sense vary in different persons? 853. Mention a condition of the brain that influences the nerves of sensation. -=-=-=-=-=-=-=-=-=-=-=-= 854. If there is compression of the brain, as when the skull-bones are depressed, or disease of this organ exists, as in severe typhus fever, impressions made upon the nerves of the skin will not be noticed. The same is true when the mind is engaged in intense thought or study; heat or cold may be so intense as to disorganize the skin, and not to be noticed. 855. The varying health or condition of the brain usually depresses or increases the sensitiveness of the skin. This is seen in grief and fear, which diminish, while hope and joy increase the impressibility of this tissue. It is not uncommon to see the unfortunate insane endure exposure to heat and cold with seeming impunity; whereas it would induce almost insupportable suffering to the sane man. Diseases of the heart, stomach, and lungs, alter the condition of the brain, and modify, to a greater or less degree, the sensitiveness of the skin. 856. _The state of the conducting nervous trunks influences the nerves of sensation._ If a nervous trunk is compressed or divided, the parts supplied by nervous filaments from this branch, will be insensible to the impressions made upon them, and consequently such impressions are not transmitted to the brain.