TOUCH. 521 



organs of the senses becoming habituated to external impressions, 

 so that these are continually less and less strong. But in old age 

 the functions of the senses grow weak, because the organs of the 

 senses diminish. The nervous filaments, and their nutrient sub- 

 stance, waste, as well as the pulpy substance in general, and all 

 the nerves begin to atrophy. Hence Pinel did not find, in the 

 labyrinth of deaf old men, the soft substance which exists in men 

 who hear. Hence the nerves of old persons are much smaller 

 than of those in the vigour of life. As this diminution does not 

 occur at the same time in all the nervous system, it follows that all 

 the functions do not decline equally at the same time, as would 

 be the case if they declined more and more only by habituation 

 to impressions. Some even explain by habit the fact of our having 

 in health no sensation of what is passing within us in our organic 

 Or automatic life. I should ascribe this rather to an original de- 

 sign of nature, which probably accomplishes it by the tenuity of 

 the filaments that communicate between the nervous system of 

 the chest and abdomen and the nervous system of the vertebral 

 column, the senses, and the brain. 



" 10. The doubleness of any sense does not prevent our sen- 

 sation of objects from being simple : in the same manner our 

 consciousness is single, notwithstanding the five different functions 

 of the senses." 



A sensation lasts a certain time after the exciting cause has 

 ceased. Thus, if a piece of wood, with one end ignited, is whirled 

 round, we see a luminous ring ; the sensation produced by the 

 wood in each point of the circle continuing till the wood arrives at 

 that point again : a rocket forms a train. A sensation is sometimes 

 renewed, as when, after having looked at the sun, we close our 

 eyes and its figure returns. According to the law of all vital excite- 

 ment, sensations are more acute the less they have been excited, 

 and vice versa. Thus, after having been in a strong light, we at first 

 see nothing on entering a darkened apartment, but gradually dis- 

 tinguish objects in it, and, on returning into the light, find the. 

 glare very disagreeable : the same tepid water feels warm to one 

 hand previously immersed in cold water, and cold to the other 

 previously placed in warm water. 



" Touch merits our first attention, because it is the first to 

 manifest itself after birth, its organ is most extensively spread 



