1865.] Arguments in Favour of Uninterrupted Circuits. 257 



matter ; but precisely in what manner, I must not now discuss. If, however, 

 the conditions which led in the first instance to the increased nutrition 

 persisted, the pressure upon the nerve-fibres might go to the extent of 

 paralyzing them, in which case the small arteries would become dilated ; 

 the capillaries must in consequence be fully distended with blood, and that 

 congestion which constitutes one of the earliest stages of inflammation as 

 it occurs in man and the higher animals, would result. 



I have already indicated the wide differences in structure, mode of growth, 

 and in the changes occurring during action, between the spherical and oval 

 nerve-cells, and the so-called caudate nerve-cells. These differences are 

 sufficiently marked to justify me in regarding them as two distinct classes 

 of central nerve-cells performing very different offices or functions*. 



Several considerations have led me to conclude that the oval and spheri- 

 cal ganglion-cells are the sources of nervous power, while the so-called 

 caudate nerve-cells in the cerebro-spinal centre are the points at which 

 several different nerve-circuits intersect, and probably act and react upon one 

 another. The marvellously complex and combined nervous actions depend, 

 in all probability, upon the perfection attained by this latter part of the 

 nervous mechanism. I have been led further to the opinion, not only 

 that the spherical and caudate nerve-cells are concerned with the reflex 

 phenomena of the vascular system, but that those forming the ganglia on 

 the posterior roots of the spinal nerves are intimately connected with the 

 general reflex actions occurring in the voluntary muscles when the cord is 

 divided transversely. From the arrangement of the vascular nerves dis- 

 tributed to the vessels of muscles, it is easy to understand how, by an 

 increased action of these vascular nerves, the contraction of the muscles 

 of a limb might be caused. I have demonstrated that connexions exist 

 between the peripheral portion of purely sensitive nerves and the nerve- 

 fibres distributed to the tissues in which capillaries ramify, as well as to 

 capillary vessels themselves. These connexions would account for the 

 excitation of involuntary reflex actions by the application of a stimulus to 

 the general cutaneous surface. If this view be correct, the ganglia on the 

 posterior roots of the nerves, rather than the different segments of the 

 spinal cord, must be regarded as the centres of reflex actions and also as the 

 nervous centres which, with the so-called sympathetic ganglia, preside 

 over all the vascular, and, through the vessels, over the nutritive pheno- 

 mena of the body. The facts and arguments in favour of these general 

 conclusions will form the subject of a separate memoir. 



Arguments in favour of uninterrupted circuits, deduced from an examina- 

 tion of the trunks of nerves, and arrangement of nerve-centres. 



One is somewhat surprised that the mode of branching of nerves, referred 

 to generally in pp. 239, 240, which is so universal, has not been dwelt upon 



* See my paper " On the Apolar, Unipolar, and Bipolar Nerve-cells," &c., Phil. Trans. 

 1863, and a paper entitled " Indications of the Paths taken by the Nerve-currents," &c., 

 Proceedings of the Koyal Society, yol. xiii. p. 386. 



