4:78 THE SPECIAL SENSES. 



CHAPTER VI. 



\ 



THE SPECIAL SENSES. 



GENEKAL AND SPECIAL SENSIBILITY. We have already seen 

 that there exists, in the general integument, a power of sensation, by 

 which we are made acquainted with surrounding objects and some 

 of their most important physical qualities. By this power we feel 

 the sensations of heat and cold, and are enabled to distinguish 

 between hard and soft substances, rough bodies and smooth, solids 

 and liquids. This kind of power is termed General Sensibility, 

 because it resides in the general integument, and because by its 

 aid we obtain information with regard to the simplest and most 

 material properties of external objects. 



The general sensibility, thus existing in the integument, is an 

 endowment of the sensitive nerves derived from the cerebro-spinal 

 system. These nerves ramify in the substance of the skin, and by 

 subsequent inosculation form a minute plexus in the superficial 

 portions of the tissue of the corium. From this plexus, the ulti- 

 mate filaments, reduced to an exceedingly minute size, pass up- 

 ward into the conical papilla with which the free surface of the 

 corium is covered. In the papilla the nervous filaments terminate, 

 sometimes by loops returning upon themselves, and sometimes ap- 

 parently by free extremities. The papillse are also supplied with 

 looped capillary bloodvessels, and are capable of receiving an 

 abundant vascular injection. 



These papillae appear to be the most essential organs of general 

 sensation, since the sensibility of the skin is most acute where they 

 are most abundant and most highly developed, as, for example, on 

 the palm of the hand and the tips of the fingers. 



The best method of measuring accurately the sensibility of dif- 

 ferent regions is that adopted by Professors Weber and Valentin. 

 They applied the rounded points of a pair of compasses to the 

 integument of different parts, and found that if they were held 

 very near together they could no longer be distinguished as sepa- 



