372 THE MICROSCOPE. 



pressure of the thin glass, when placed on the nerve-fibre, causes nearly 

 the whole of the contents to flow out in the form of a granular material ; 

 it therefore becomes requisite to exercise more care in the breaking up 

 of structures to view these tubules, which should be immersed in a 

 very weak solution of spirit and water. Mr. Clarke, in his very im- 

 portant investigations on the structure of the spinal cord, placed the 

 cord, immediately after removal from the animal, into strong spirits of 

 wine. This hardened it, and enabled him to make very thin sections of 

 the spine. As nerves approach the brain or spinal cord, they gra- 

 dually become smaller, and do not measure more than from l-10,000th 

 to l-14,000th of an inch in diameter. The difference in the nervous 

 substances is not an affair of colour only ; it refers also to their intimate 

 structure and organisation : the white matter is made up of bundles of 

 tubular fibres ; whilst the grey is composed of aggregated cells, and is 

 often denominated the vesicular neurine. To collections of this vesi- 

 cular substan\;e the term " ganglion" is applied ; because the knots of 

 nervous matter, which were formerly supposed to give origin to the 

 nerves, and which are distributed so largely throughout the body, are 

 vesicular in their composition. And thus the identity in structural 

 constitution has led to the employment of the word ganglion as a 

 common term ; although the ganglionic or spheroidal form is not at 

 all essential, as was at one time supposed, to the constitution of what 

 is now called ganglionic substance. Physiological and pathological 

 researches have rendered it more than probable that the vesicular and 

 the fibrous substances have universally separate and distinct ofiices in 

 the animal economy ; the ganglionic structures being the source of 

 functional change, and the fibrous matter being simply for the conduc- 

 tion of impressions originating in the former. This theory, in the 

 promulgation of which Mr. Solly shares probably in the most eminent 

 degree, is now received very generally as a scientific truth. The 

 nerve-coi-puscles and stellate nerve-fibres are represented in Plate XII. 

 No, 10. 



All the sensory ganglia, it may here be noticed, besides their in- 

 strumentality in inducing the simpler forms of consciousness, react 

 upon the muscular system, when stimulated from without ; and that, 

 too, in apparent independence of thought or volition. The movements 

 thus arising Dr, Carpenter very aptly designates consensual : they are 

 seen when the dazzled eye withdraws instinctively from the light, or 

 when the startle follows upon a loud and unexpected sound. 



Consolidated l^issues. — These tissues are formed by a chemical com- 

 bination with the gelatine of the fibre, which in cartilaginous forma- 



