380 



SPECIAL HISTOLOGY. 



diameter of 0-0012 of a line, and in this state enter the external gray 

 layer. This layer, although to outward appearance everywhere per- 

 fectly homogeneous, consists of two not well-defined laminae, the inner 

 of which contains nerve-fibres and very well-marked, large nerve-cells, 

 whilst the outer presents nothing but a finely- granular, pale, light-yel- 

 lowish substance, which is distributed generally throughout this gray 

 layer, and contains no nerve-cells. The granular substance agrees 

 chemically, morphologically, and physically in all respects with the 

 already-described contents of the nerve-cell ; it is tenacious, elastic, 

 rendered more opaque by acetic acid, and more transparent in caustic 

 soda, in which it is, for the most part, dissolved, and exists in the purest 

 form in the outer half of the gray layer, that is to say, next to the pia 

 mater. The small nerve-cells, speaking generally, are very few in 

 number and indistinct. They occur scattered throughout the gray layer, 

 having a diameter of 0-004-0-008 of a line, more frequent towards the 

 ferrugineous layer than more externally, and when successfully prepared, 

 particularly by means of chromic acid, most of them exhibit delicate 

 processes, which, however, can never be traced to any distance, and are 

 frequently torn off close to the cells. Besides these cells, there also 

 occur here and there, but on the whole rarely, nuclei of 0-002-0-0048 



Fig. 148. 



of a line, which, to all appearance, are free, as they are met with even 

 in the most carefully -made preparations. Entirely different from these 

 smaller elements, and very peculiar, are the large cells of the gray layer 

 (Fig. 148) discovered by Purkinje. These cells, measuring 0-016-0-03 

 of a line, and of a round pyriform or oval figure, with finely-granular, 

 colorless contents, occur only in the innermost portions of the gray, 



FIG. 148. Large cells of the gray layer of the cortical substance of the human cere- 

 bellum, magnified 350 diameters. 



