THE SENSES. 489 



the chest and neck fixed, and speaking with the mouth almost 

 closed, and the lips and lower jaw as motionless as possible, 

 while air is very slowly expired through a very narrow glottis ; 

 care being taken also, that none of the expired air passes 

 through the nose. But, as observed by Mu'ller, much of the 

 ventriloquist's skill in imitating the voices coming from par- 

 ticular directions, consists in deceiving other senses than hear- 

 ing. We never distinguish very readily the direction in which 

 sounds reach our ear ; and, when our attention is directed to a 

 particular point, our imagination is very apt to refer to that 

 point whatever sounds we may hear. 



The tongue, which is usually credited with the power of 

 speech language and speech being often employed as synony- 

 mous terms plays only a subordinate, although very impor- 

 tant part. This is well shown by cases in which nearly the 

 whole organ has been removed on account of disease. Patients 

 who recover from this operation talk imperfectly, and their 

 voice is considerably modified ; but the loss of speech is con- 

 fined to those letters, in the pronunciation of which the tongue 

 is concerned. 



CHAPTER XIX. 



THE SENSES. 



SENSATION consists in the mind receiving, through the me- 

 dium of the nervous system, and, usually as the result of the 

 action of an external cause, a knowledge of certain qualities 

 or conditions, not of external bodies but of the nerves of sense 

 themselves ; and these qualities of the nerves of sense are in 

 all different, the nerve of each sense having its own peculiar 

 quality. 



There are two principal kinds of sensation, named common 

 and special. The first is the consequence of the ordinary sen- 

 sibility or feeling possessed by most parts of the body, and is 

 manifested when a part is touched, or in any ordinary manner 

 is stimulated. According to the stimulus, the mind perceives 

 a sensation of heat, or cold, of pain, of the contact of hard, 

 soft, smooth, or rough objects, &c. From this, also, in morbid 

 states, the mind perceives itching, tingling, burning, aching, 

 and the like sensations. In its greatest perfection, common 

 sensibility constitutes touch or tact. Touch is, indeed, usually 

 classed with the special senses, and will be considered in the 

 same group with them ; yet it differs from them in being a 

 property common to many nerves, e. g., all the sensitive spinal 



