THE SKIN AS AN OEGAN OP SENSE. 



Bearing in mind that all the sensory organs originate in 

 the ectoderm, we find in the skin even of the highest animals 

 the power to give the central nervous system such sense-im- 

 pressions as bear a relation to the original undififerentiated 

 sensations of lower forms as derived from the general surface 

 of the body, but with less of specialization than is met with in 

 the sense of hearing and vision, so that it is possible to under- 

 stand how it is that the skin must be_regarded not only as the 

 original source of sensory impulses for the animal kingdom, 

 but why it still remains perhaps the most important source of 

 information in regard to the external world, and the condition 

 of our own bodies; for it must be remembered that the data 

 afforded for sensory judgments by all the other senses must 

 be interpreted in the light of information supplied by the skin. 

 We really perceive by the eye only retinal images. The dis- 

 tance, position, shape, etc., of objects are largely determined by 

 feeling them, and thus associating with a certain visual sensa- 

 tion others derived from the skin and the muscles, which latter 

 are, however, generally also associated with tactile sensations. 



It is recorded of those blind irom birth that, when restored 

 to sight by surgical operations, they find themselves quite un- 

 able to interpret their visual sensations; or, in other words, 

 seeing they do not understand, but must learn by the other 

 senses, especially tactile sensibility, what is the real nature of 

 the objects that form images on their retinae. All objects seen 

 appear to be against the eyes, and any idea of distance is out of 

 the question. 



Special forms of end-organs are found scattered over the 

 skin, mucous and serous surfaces of the body, such as Pacinian 

 corpuscles, touch-corpuscles, end-bulbs, etc. ; while in lower 

 forms of vertebrates many others are found in parts where sen- 

 sibility is acute. There seems to be little doubt that these are 



