DISTRIBUTED TO THE CAPILLARY VESSELS. 821 



concerned in special sensation. We know that many 

 of the ultimate parts of organs which take part in 

 sensation — which, indeed, constitute the active por- 

 tion of the sensitive apparatus, are destitute of vessels 

 altogether. These and other considerations render it 

 almost certain that the nerve-fibres of the capillaries 

 are not nerves of sense. 



Are they motor ? — The capillaries are not provided 

 with muscular fibres, nor is there any contractile 

 tissue to be demonstrated in connection with them. 

 Although it has been confidently asserted that the 

 capillary walls consist of protoplasin (!), anyone who 

 will be at the pains of examining actual capillaries, 

 as, for example, those of the pia mater, will soon be 

 convinced that this view is a mistake. It is, as I have 

 shovTn, one of those conjectural anatomical observa- 

 tions which are in favour in these days. An hypo- 

 thesis was advanced to account for the passage of 

 blood coi-puscles through the capillary walls, and this 

 and other hypotheses rendered it necessary that some 

 one should demonstate the lyrotajplasraiG character of 

 the ca.jnllary vjalls. Protoplasm has been therefore 

 conjecturaily discovered in the capillaries by more 

 than one microscopical philosopher. 



The memhrane of which the walls of capillaries are 

 in part composed can be seen, and the bioplasts con- 

 nected with it demonstrated in considerable number, 

 and without difficulty. The membrane is transpa- 

 rent, slightly fibrous in the vessels of old animals, 

 highly elastic, but destitute of any structure that can 

 be regarded as contractile. We may therefore, I think, 

 dismiss the idea that these nerve-fibres are motor,or 

 are in any way concerned directly, — that is, by any 

 influence exerted by them on the walls of the capil- 

 laries, — in reducing the calibre of these minute ves- 

 sels. If protoplasm could only be proved to exist in 

 the walls of the capillaries, the presence and action 

 of the nerve-fibres would be accounted for. It would 



