236 Causes and Course of Organic Evolution 



McCliire had earlier readied the condusion, for the nerve- 

 cells of Gasteropoda, that the granular substance "is homol- 

 ogous with that found in the nerve-cells of vertebrates (Nissl 

 bodies)" (85: 13). 



Various and important papers have appeared on the Nissl 

 granules of vertebrates, some of which deal A^nith histological 

 details, others with histo-physiological changes. Under the 

 latter head several observers have reached the common con- 

 clusion that, after section of ganglionic cells, degenerative 

 changes occur in one to four days, that result in "a progressive 

 solution of the tigroid (Nissl) substance, beginning either 

 near the nucleus or at a point intermediate between the nucleus 

 and the periphery of the cell. The cell becomes swollen, 

 and the nucleus more or less displaced toward the periphery." 

 (S6, 18: 101; 19: 125.) "When in time repair may occur such 

 consists of a restoration of the Nissl bodies and a return of 

 the nucleus to the center of the cell." 



Ranson {supra, also V. 18) not only agrees Tvitli his prede- 

 cessors Lugaro, Cox, Warrington, and Griffiths, as to the 

 existence of several types of nerve-cell, specially the "small" 

 and "large" cells, but also concludes that in the former the 

 most rapid and extensive changes occur, wliile in the latter 

 the changes are slower. He has also traced the successive 

 integrative developments toward regeneration in young rats 

 "that began on the eighth or ninth day and was almost com- 

 plete in twenty days." During reformation of the Nissl gran- 

 ules these gradually increased in number and size, so that 

 "by the seventeenth day the central portions of the cells con- 

 tain Nissl-bodies of considerable size, and by the twentieth 

 day the distinction between the coarsely granular peripheral 

 ring and the rest of the cell has disappeared." 



But the observations of the above-named, and of other in- 

 vestigators such as Holmgren, Hamaker, and Rand, suggest 

 that each ganglion cell is traversed by a fine network system 

 of threads, as well as by a system of canals, which seem both 

 to be intimately related to the Nissl or neuratin substance. 

 There are thus represented in each nerve celL apart from the 



