INADEQUACY OF NATURAL SELECTION, ETC. G05 



tised in tactual exploration than the fingers of those who can see, 

 acquire greater discriminativeness : especially the fingers of those 

 blind who have been taught to read from raised letters. Not 

 wishing to trust to this current belief, I recently tested two 

 youths, one of fifteen and the other younger, at the School for 

 the Blind in Upper Avenue Road, and found the belief to be 

 correct. I found that instead of being unable to distinguish 

 between points of the compasses until they were opened to one- 

 twelfth of an inch apart, both of them could distinguish between 

 points when only one-fourteenth of an inch apart. They had 

 thick and coarse skins ; and doubtless, had the intervening 

 obstacle, so produced, been less, the discriminative power would 

 have been greater. It afterwards occurred to me that a better 

 test would be furnished by those whose finger-ends are exercised 

 in tactual perceptions, not occasionally, as by the blind in read 

 ing, but all day long in pursuit of their occupations. The facts 

 answered expectation. Two skilled compositors, on whom I 

 experimented, were both able to distinguish between points when 

 they were only one-seventeenth of an inch apart. Thus we have 

 clear proof that constant exercise of the tactual nervous struc 

 ture leads to further development.* 



Now if acquired structural traits are inheritable, the various 

 contrasts above set down are obvious consequences ; for the 

 gradations in tactual perceptiveness correspond with the grada 

 tions in the tactual exercises of the parts. Save by contact with 

 clothes, which present only broad surfaces having but slight and 

 indefinite contrast, the trunk has scarcely any converse with 



* Let me here note in passing a highly significant implication. The 

 development of nervous structures which in such cases take place, cannot 

 be limited to the linker-ends. If we figure to ourselves the separate sensi 

 tive areas which severally yield independent feelings, as constituting a net 

 work (not, indeed, a network sharply marked out, but probably one such that 

 the ultimate fibrils in each area intrude more or less into adjacent areas, so 

 that the separations arc indefinite), it is manifest that when, with exercise, the 

 structure has become further elaborated, and the meshes of the network 

 smaller, there must be a multiplication of fibres communicating with the cen 

 tral nervous system. If two adjacent areas were supplied by branches of one 

 fibre, the touching of either would yield to consciousness the same sensation: 

 there could be no discrimination between points touching the two. That 

 there may be discrimination, there must be a distinct connection between each 

 area and the tract of grey matter which receives the impressions. Nav more, 

 there must be, in this central recipient-tract, an added number of the separate 

 elements which, by their excitements, yield separate feelings. So that this in 

 creased power of tactual discrimination implies a peripheral development, a 

 multiplication of fibres in the trunk-nerve, and a complication of the nerve- 

 centre. It can scarcely be doubted that analogous changes occur under 

 analogous conditions throughout all parts of the nervous system not in its 

 sensory appliances only, but in all its higher co-ordinating appliances, up to 

 the highest. 



