THE JVA Y IN. 787 



Hall's studies began, apparently in ignorance of much preceding knowledge. 

 New points he ascertained are the tonic closure of the sphincters by 

 reflex action, the cessation of strychnia convulsions on destruction of the 

 spinal cord, and the easier excitation of reflexes by stimulating the end 

 apparatus of nerves, than by stimulation of the nerve trunks themselves. In 

 his own estimation, Hall's chief advance lay in the finding of evidence of 

 separate nerve paths for reflexes unaccompanied by sensation, and apart 

 from paths subserving sensation and volition. His evidence was not very 

 satisfying, but it led to work by Grainger (1837), in which good proof 

 was given that in the cord the sole seat of reflex centres is the grey matter ; 

 and, further, that each afferent root sends some fibres direct into the grey 

 matter for reflex action, and some fibres upwards as a strand in the white 

 matter, subserving the elaboration of sensation. Valentin suggested two years 

 later that the nerve cells in the grey matter are structures for transferring 

 impulses from the afferent to the efferent channels. Lastly, with the elder 

 Waller's l discovery of degeneration of nerve fibres after section, came demon- 

 stration of the functional and morphological continuity between the conducting 

 channels and their respective groups of nerve cells. The question of the action 

 of ganglia as reflex centres was, for the spinal ganglia, answered in the negative 

 in Johann Midler's text-book (1837). For the ganglia of the sympathetic an 

 answer in the affirmative was declared by Henle, 2 Stilling, 3 Claude Bernard, 4 

 and others 5 ; but except in a modified sense of the term " reflex centre," such 

 as is afforded by the interpretation offered by Langley, 6 its substantiation seems 

 unlikely. The ganglia of invertebrata were at first supposed — chiefly owing 

 to Newport's 7 conclusions — to be like the spinal ganglia, not seats of reflexion ; 

 but Carpenter 8 later proved them to have reflex powers, and pointed out their 

 analogy with the spinal centres and brain, a view to which Newport subse- 

 quently gave adherence. 9 



The Way In. 



The peripheral afferent channel consists always of an elongated 

 nerve cell, which by one of its ends extends to points accessible to 

 the environment, including in the environment the " material me," 

 and by the other end lies deeply embedded in linkage with other 

 nerve cells of various rank, composing the machinery of the central 

 nervous system. These nerve cells together form, therefore, the first 

 part of the path travelled by waves of change constantly poured into 

 the nervous system by the world of changing energy around it. These 

 are the " primary afferent neurones " or the " afferent root cells." Their 

 cell branches are as nerve fibres much commingled in most places with 

 those of efferent and other nerve cells, but their cell bodies (perikarya) 

 are collected apart into ganglia, which they thus form. 



Assuming the whole organisation to consist of a fore and aft series of 



1 Phil. Trans., London, 1850, pt. 2, p. 423; Corrupt, rend. Acad. d. sc, Paris, 1851, 

 tome xxxiii. p. 606 ; Arch. f. Anat., Physiol, u. wisscnsch. Med., 1852. 



2 "Patholog. Untersuch.," Berlin, 1840. 3 "Physiol. Untersuch.," Leipzig, 1840. 



4 Compt. rend. Acad. d. sc, Paris, 1862, tome ii. p. 341. 



5 Sokownin, Arch. f. d. ges. Physiol., Bonn, Bd. viii. S. 600 ; Nussbaum, Arb. d. Lab. 

 d. Warschauer Med. Fac, 1879, Bd. v. S. 120 ; lately by Nawrocki and Skabitschewsky, 

 Arch. f. d. ges. Physiol., Bonn, Bd. xii. S. 141 ; Langley and Anderson, Journ. Physiol., 

 Cambridge and London, 1894, vol. xv. p. 11, and vol. xvi. p. 410 ; Griffiths, Journ. Anat. 

 and Physiol., London, 1895, vol. xxix. p. 61 ; C. C. Stewart, Am. Journ. Physiol., vol. ii. 

 p. 186. 



6 See this Text-Book, article " Sympathetic," p. 678. 



7 Phil. Trails., London, 1832-43. 



8 "The Physiology of the Nervous System of Invertebrated Animals," London, 1839. 

 a "Nervous System of Myriapoda," Phil. Trans., London, 1843. 



