360 Journal of Comparative Neurologv. 



adult cortex — "pure yellow;" "more yellow than gray;" "yellow- 

 gray;" "moregray than yellow;" and "pure gray. "^ Each of the 

 various regions examined was classified under one of these 

 colors. In dealing with the i ]^ year child cortex, tins classi- 

 fication could not be applied, because the child cortex appears 

 pure yellow to macroscopic observation in all regions. Differ- 

 ences in shade which offer a basis for an analogous treatment of 

 the child cortex, do, however, occur in the medullary center, 

 which, in the adult is a uniform gray. The shades distinguished 

 in the medullary center of the child were, "light gray," "gray," 

 "blackish," "black," and "deep black. "^ 



The microscopic investigation consisted in noting the num- 

 ber of distinguishable layers differentiated by the stain in each 

 region, measuring the thickness of each layer and recording the 

 characteristics of the fibers composing each layer. ^ 



The general result of the macroscopic investigation was to 

 show that the development of intra-cortical fibers continues 

 much later in life than had previously been supposed. In the 

 child brain, the cortex is uniformly yellow, showing an almost 

 complete lack of meduUated fibers. A comparison of an 18-year 

 cortex with a 38-year cortex showed that there was 50% less 

 of the pure yellow substance in the 38-year cortex than in the 

 1 8-year cortex, and 50% more of the "more-gray-than-yellow, " 

 and "gray" substance, indicating a marked development 

 in the number of intra-cortical fibers between 18 and 38 years. ^ 

 The microscopic investigation revealed an increase in the num- 

 ber of functional fibers up to the age of about 45 to 50 years. ^ 



The more important and detailed results come from the 

 microscopic investigation, Kaes divides the fibers of the cortex 

 into three main typical layers, which are characteristic of all 



' 3. p- 35 ; P- 64. 

 '5. P- 30; P- 50. 

 » 3, p. 5 ; pp. 8-33. 

 *3. p. 35; 2. P- 2- 

 » 4, p. 2 ; 6, p. 5. 



