4 Mason — Central Nervons System of Reptiles, etc. 



between the brachial and crural nuclei. It might seem fair to 

 inter, therefore, that the nucleus of a motor cell grows with 

 the muscular substance which it is su|>posed to innervate. If 

 farther research confirm this inference, a conclusive reason 

 will be furnished for the now common division of nei've-celis 

 into motor and sensitive; for if the nuclei of a definite cell- 

 group are found to increase in size along with the develop- 

 ment of muscular power in the related extremities, and to 

 have no such coimection with the function of sensation, such 

 nuclei may certainly be regarded as belonging to the motor 

 apparatus. 



A word as to the manner of making permanent preparations 

 for counting and measuring nuclei. During the past winter 

 I have tried the method recommended by Stieda* for hard- 

 enins: the brains and cords of small animals, and have found 

 it to be superior to any other that I have yet met with. In 

 transparent carmine-colored sections the nuclei are sliowii 

 with remarkable distinctness, and can be measured with 

 great ease and accurac3^ My custom has been to make an 

 unbroken series of transverse cuts through both the enlarge- 

 ments ; mount all the sections, and carefully label all the 

 slides so that all the preparations from the same individual 

 may be kept together by themselves. Longitudinal sections? 

 are particularly well adapted for showing a large number of 

 nuclei in the same field. 



It is always desirable to measure fresh nuclei when possible. 

 This I have done in the frog and alligator, confirming what was 

 observed in sections. Great care must be taken here to a\oid 

 compressing the nucleus between the cover and slide, and tor 

 this purpose it is always better to use bits of softened wax to 

 support the cover under its four corners. 



When the sections are mounted and the Canada balsam 

 has become sufticiently hard the slide is placed under the No. 



5 objective (better to have a movable stage) with micrometer 

 eye-piece t and the group of large cells in one of the inferior 

 horns is readily found. The nuclei of tliese cells are then 



*8ee this journtil for January, 1880. 



f Vid. Robin — Traite du Microscope, p. 208. 



