Febbuaet 15, 1918] 



SCIENCE 



153 



did not come into general use till nearly a 

 decade and a half later. Nevertheless, as 

 soon as it was generally applied, it yielded 

 such important results that in May, 1891, 

 Kolliker could substantiate the claim that 

 every nerve fiber in the body was at some 

 part of its course directly connected with 

 a ganglion cell, and in June of the same 

 year Waldej'er, on the basis of conclusions 

 drawn largely from Golgi preparations, 

 promulgated the theory of the neurone, the 

 first consistent account of the nerve cell. 



According to this well-known doctrine 

 the ganglion cell of the older workers is 

 really the nucleated body of the true nerve 

 cell, or neurone, whose processes may be of 

 two kinds: short, branching, protoplasmic 

 extensions, the dendrites; and long, un- 

 branched, nerve-fiber processes, the neu- 

 rites. As all nerve fibers were believed to 

 be thus related to nerve cells they were at 

 once classed as a special type of cell process. 

 Further, the fibrillar material of the cen- 

 tral gray, the punctate substance, which 

 was regarded by Gerlach (1871) as a con- 

 tinuous network, was now looked upon as 

 the ultimate branches of the dendrites and 

 neurites, the means by which one neurone 

 is put into communication with another. 

 Hence this material was believed to be 

 broken up into appropriate neuronic sys- 

 tems separated one from another by an 

 infinitude of minute interruptions, which, 

 however, were capable of physiological con- 

 tinuity through what is known as a syn- 

 apse. Thus each neurone, or true nerve 

 cell, was believed to possess a certain 

 amount of independence from its neigh- 

 bors though physiologically united to them 

 at least by transmitting contact. This in 

 brief is the conception of the neurone, or 

 true nerve cell, a conception that has been 

 most prolific in its consequences not only as 

 a means of understanding the structural 

 relations of nervous elements but of inter- 



preting their degeneration as originally 

 outlined by Waller (1850), their regenera- 

 tion as worked out by subsequent investi- 

 gators, and their development as first 

 clearly described by His (1886). 



This conception, however, was not based 

 on what can be seen in Golgi preparations 

 only; it was confirmed and supported by a 

 great array of results such as have been 

 obtained by Ehrlich's methylen-blue treat- 

 ment and by the host of new metal-impreg- 

 nation methods modelled more or less on 

 the original Golgi procedure. 



In considering the activity of the typical 

 vertebrate neurone, it is generally recog- 

 nized that the nerve impulse enters this 

 element through its dendrites and, after 

 traversing its cell body, emerges from it 

 through its neurite. This is very clearly 

 seen in the motor neurones of the spinal 

 and the cranial nerves (Fig. 1). Here the 



Fig. 1. Diagram of the primary neurones of the 

 spinal cord; the dorsal neurone (d) extends from 

 the skin (s) to the central gray of the cord, the 

 ventral neurone (v) from the central gray to the 

 muscles (m). 



dendrites of the given neurone are in close 

 relation with the neurite processes of other 

 neurones (d) from which they receive nerve 

 impulses that are passed on through their 

 own cell body and over its neurite to be 

 discharged finally into the attached mus- 

 cle fibers (m). As in such series the den- 

 drites serve as a receptive mechanism and 

 the neurite as a discharging one, it may be 

 claimed that the neurone exhibits a kind of 

 cellular polarity in which the dendrites 



