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SCIENCE 



[N. S. Vol. XLVII. No. 1207 



prising that neurologists have devoted much 

 of their energy and time to discovering the 

 disposition and arrangements of the cells 

 in nervous organs. 



Notwithstanding the fact that the cell 

 doctrine as applied to animals was enunci- 

 ated by Schwann as early as 1839, it was 

 not till more than half a century later that 

 a clear and consistent idea of the nerve 

 cell was arrived at. The slowness with 

 which this result was attained was due to 

 the unusual form and complicated struc- 

 ture of this element. Nerve fibers, accord- 

 ing to Stieda (1899), were probably first 

 really seen and figured by the Florentine 

 physician Felix Fontana in 1781, but it was 

 not till 1833 that Ehrenberg in the prelimi- 

 nary announcement of a monumental work 

 on the fibrous structure of the central ner- 

 vous organs, described certain corpuscles 

 that proved to be what later investigators 

 called ganglion cells. The connection of 

 these two elements, vaguely intimated in 

 1838 by Remak and surmised in 1840 by 

 Hannover, was first really demonstrated 

 for invertebrates in 1842 by Helmholtz and 

 for vertebrates in 1844 by Kolliker who 

 showed that fibers with a medullary sheath, 

 and therefore unquestionably nervous, were 

 directly connected with ganglion cells. 

 From the time of these discoveries it be- 

 came necessary to assume that in some way 

 or other ganglion cells were an essential 

 element in the nervous system. Their asso- 

 ciation with ganglionic masses and other 

 deeper organs led naturally to the view 

 that they were the real centers of nervous 

 activity, the fibers being regarded as ele- 

 ments of conduction merely. Hence arose 

 that infinite collection of diagrams of ner- 

 vous mechanism devised by the neurologists 

 and copied by the physiologists and psy- 

 chologists of some two generations ago and 

 consisting usually of an afferent fiber lead- 

 ing from the periphery to a centrally situ- 



ated ganglion cell from which in turn an 

 efferent fiber stretched out to a muscle or 

 other like end-organ. 



But the nervous system is not con- 

 structed upon so simple a plan. In 1847 

 Wagner showed that the ganglion cells in 

 the electric lobes of the torpedo exhibited 

 two types of processes. These were subse- 

 quently designated as protoplasmic and 

 nerve-fiber processes by Deiters (1865), 

 who attempted to support the generaliza- 

 tion that every ganglion cell possessed both 

 types of processes. 



Not only did complications grow in these 

 directions, but in 1855 Leydig discovered 

 in the ganglionic bodies of spiders what 

 appeared to be a finely granular material 

 which he called punctate substance. Simi- 

 lar material was also shown to be a consid- 

 erable constituent in the gray matter of 

 the vertebrate nervous system. Hence, in 

 addition to nerve fibers and ganglion cells, 

 a third kind of material was shown to be 

 present in many nervous organs. 



This material, as was subsequently dem- 

 onstrated by Gerlach (1871) and others, 

 consisted in reality of very fine fibrils 

 which when seen in section appeared as mi- 

 nute points ; hence Leydig 's name for it of 

 punctate substance. From these very fine 

 fibrils nerve fibers were seen to take their 

 origin and thus arose the dispute over the 

 direct and the indirect origin of nerve 

 fibers, that is, their origin directly from 

 ganglion cells or indirectly from these cells 

 through the intervening fibrillar substance. 



The confusion to which this discussion 

 led was cleared up and swept away by the 

 introduction of the Golgi method of silver 

 impregnation, a method that yielded prepa- 

 rations so marvelously clear and sharp that 

 for the first time the relations of nerve 

 fibers, ganglion cells, and fibrillar material 

 seemed within grasp. Although this 

 method was described as early as 1873, it 



