268 NATURE AND MAN. 



two forms of nerve-tissue respectively receive, is not less significant 

 than that of their histological characters ; this being especially 

 manifest in the "grey "and the "white " portions of the brain. 

 For, whilst the nerve-cells lie in the midst of a plexus of capillaries 

 so close that no other tissue receives anything approaching to the 

 same quantity of blood in a given space, the vascularity of the 

 tubular component of the brain, spinal cord, and nerve trunks is 

 by no means remarkable. And it is easily proved experimentally 

 that, while an interruption to the circulation of the blood through 

 the brain immediately suspends its functional activity, the con- 

 ductivity of the nerve-trunks lasts for a considerable time after the 

 general stoppage of the flow of blood through their vessels. 



I can myself distinctly recollect the gradual spread of the belief 

 in the physiological distinctness of these two forms of nerve- 

 substance (of which the late Mr. S. Solly was one of the earliest 

 upholders in this country) from a very limited circle to universal 

 acceptance ; the tubular being regarded, like the wires of the 

 electric telegraph, as the conductor of nerve-force ; whilst the 

 vesicular or ganglionic was considered, like the battery which 

 sends the charge, as the origifiator of nerve-force. We now know 

 that this account of the matter is not strictly true ; since the 

 vesicular substance may serve also for the transmission, while the 

 fibrous substance may, under certain circumstances, serve also for 

 the origination, of that special form of " molecular motion " which 

 constitutes the characteristic action of the nervous system. But 

 in a broad, general way, the analogy is sufficiently correct ; and the 

 recognition of it soon led to important consequences. For Mr. 

 R. D. Grainger showed, by a careful examination of the roots of 

 the spinal nerves, that while some of them are continuous with the 

 fibrous strands of the cord, which thus bring them into continuous 

 connection with the cephalic centres, others lose themselves in its 

 grey or vesicular nucleus, which, serving as their ganglionic centre, 

 is the source of the independent power of the spinal cord ; and 

 he further pointed out that the relative proportions of this vesicular 

 matter in the several parts of tlie spinal cord of different vertebrate 

 animals is closely proportioned to the size of the trunks which 

 proceed from them, and more particularly to the relative importance 

 of the anterior and posterior members as instruments of locomo- 



