104 Journal of Comparative Neurology. 



Also, after trying several formulae, the developer which gave 

 the best satisfaction was made according to the " Bromo-hydro- 

 chinon " formula which accompanies these plates. 



The apparatus used was the large photographic and projec- 

 tion outfit manufactured by Zeiss. This was mounted on a 

 large stone pillar which insured the perfect steadiness of the ap- 

 paratus. 



The sections were photographed under a magnification of 

 from 500 to 800 diameters and the exposure made according to 

 the intensity of the light. A small diaphragm and long expos- 

 ure gave the best results. The source of light was an ordi- 

 nary Welsbach burner. 



The Printing. 



Each negative of a section was labeled with the weight of 

 the frog, the number of the nerve and with the region and level 

 from which the section was taken. This label was cut through 

 the film on one corner of the negative so that in the printing 

 the label would print also. 



That grade of velox paper sold under the name " Carbon 

 Velox" was found best suited for reproduction, since pure blacks 

 and whites can be obtained with ;it. Plates IX, XI, and XIII 

 are reproductions of prints made with this paper. Blue prints 

 were used almost exclusively in the counting procedure. Blue 

 print paper is easier to manipulate and if a good quality be used, 

 prints can be obtained possessing a high degree of sharpness 

 and detail. 



The Method of Counting. 



The method employed was devised in this laboratory and 

 has not been previously described. In order to count a giv- 

 en section, a photograph of it was fastened upon a small board 

 of soft wood, the section itself placed under the microscope and 

 the two oriented. With a sharp pointed pencil, the photograph 

 was marked off into fields of small area the boundaries of which 

 were determined by the grouping of the fibers. 



The section, kept under the microscope for reference, was 

 subjected to an enlargement of 640 diameters or an enlarge- 



