182 . PHYSIOLOGY 



there being a deficiency in the sense of smell in the human species ; 

 and we find that the tongue in the human species is better calculated 

 for taste than it is in many other animals. Its surface is vastly 

 increased by the villi and papillae, and by its cuticle being very thin. 

 It is of considerable use in the first operations of deglutition, such as 

 the management of the food in the operation of mastication, and, when 

 the food is masticated, to conduct it to the oesophagus. It makes, per- 

 haps, a principal part of the instrument of sound. The other uses 

 (which in many other animals are considerable) are but few in man, 

 the hand supplying the deficiency. 



Of the Progress of the Senses, especially Taste. 



It is some time before children are sensible of different sensations ; 

 everything that strikes the senses is the same ; but by degrees they 

 begin to distinguish and separate one from the other ; first, by the 

 agreeable and disagreeable [impressions]. A new-born child is not 

 sensible of taste : all tastes are alike : the whole business of a child, 

 at first, is to swallow everything that touches the lips ; nor have they 

 at this time the power of rejection. 



A child laughs when it is but a few days old ; and this cannot arise 

 from any pleasing ideas, as it cannot have formed any ; but it must 

 arise from an agreeable state of body : not from mere absence of 

 uneasiness, or perfect tranquillity, or insensibility, but from a certain 

 irritation that is agreeable, without thought. Some sounds have the 

 same effect at so early an age. Children swallow whatever is put into 

 their mouth, let it be ever so (what we call) ill-tasted ; this shows that 

 taste is some time in forming, and requires a variety of impressions to 

 cause even agreeable and disagreeable tastes ; besides, at first children 

 have not the power of rejecting ; they gain that by habit. 



Relative Durability of Impressions in the different Organs of Sense. 



The sense of smell is the least durable of any ; when the application 

 is continued we very soon lose the sense of it. Taste has something of 

 the same kind. Sight is the most permanent ; we always see when the 

 object strikes the organ of sight, excepting when the mind is attending 

 to something else, or when the organ is tired, as when going to sleep. 



Of the Organ of Touch. 



Although every part of an animal feels, yet the skin and all exposed 



parts are perhaps the most sensible of the simple impressions of touch*, 



and not only most sensible, but most capable of distinguishing the 



* Here I would be understood to make a material distinction between the sensa- 

 tion of touch, and irritation to action or pain. 



