THE SENSES. 159 



for their adjustment to various purposes standing, walking, grasping, 

 etc. This muscular sensibility is shown in our power to estimate the dif- 

 ferences between weights by the different muscular efforts necessary to 

 raise them. Considerable delicacy may be attained by practice, and the 

 difference between 19 oz. in one hand and 20 oz. in the other is readily 

 appreciated (Weber). 



This sensibility with whicn the muscles are endowed must be carefully 

 distinguished from the sense of contact and of pressure, of which the 

 skin is the organ. When standing erect, we can feel the ground (con- 

 tact), and further there is a sense of pressure, due to our feet being 

 pressed against the ground by the weight of the body. Both these are 

 derived from the skin of the sole of the foot. If now we raise the body 

 on the toes, we are conscious (muscular sense) of a muscular effort made 

 by the muscles of the calf, which overcomes a certain resistance. 



(2.) Special Sensations. Including the sense of touch, the special 

 senses are five in number Touch, Taste, Smell, Hearing, Sight. 



Difference between Common and Special Sensations. The 

 most important distinction between common and special sensations is that 

 by the former we are made aware of certain conditions of various parts of 

 our bodies, while from the latter we gain our knowledge of the external 

 world also. This difference will be clear if we compare the sensations of 

 pain and touch, the former of which is a common, the latter a special 

 sensation. "If we place the edge of a sharp knife on the skin, we feel 

 the edge by means of our sense of touch; we perceive a sensation, and refer 

 it to the object which has caused it. But as soon as we cut the skin with 

 the knife, we feel pain, a feeling which we no longer refer to the cutting 

 knife, but which we feel within ourselves, and which communicates to 

 us the fact of a change of condition in our own body. By the sensation 

 of pain we are neither able to recognize the object which caused it, nor 

 its nature" (Weber). 



General Characteristics: Seat. In studying the phenomena of 

 sensation, it is important clearly to understand that the Sensorium, or 

 seat of sensation, is in the Brain, and not in the particular organ (eye, 

 ear, etc.) through which the sensory impression is received. In com- 

 mon parlance we are said to see with the eye, hear with the ear, etc., but 

 in reality these organs are only adapted to receive impressions which are 

 conducted to the sensorium, through the optic and auditory nerves re- 

 spectively, and there give rise to sensation. 



Hence, if the optic nerve is severed (although the eye itself is per- 

 fectly uninjured), vision is no longer possible; since, although the image 

 falls on the retina as before, the sensory impression can no longer be con- 

 veyed to the sensorium. When any given sensation is felt, all that we can 

 with certainty affirm is that the sensorium in the brain is excited. The 

 exciting cause may be (in the vast majority of cases is), some object of 



