GASSEEIAN GANGLION: ALBINO RAT 233 



One old rat, 485 days of age, was used for both purposes and 

 therefore the total number of individual rats was seventy-six. 

 To obtain accurate results two rats of like age were employed 

 where possible. The only exception was in the case of the last 

 pair, which were not of like age, one being 385 and one 485 days 

 old. 



All the rats were killed with ether and the body weight and 

 body length recorded, as in tables 1 and 2. The thoracic and ab- 

 dominal organs were carefully examined, and then after the 

 removal of the brain the gasserian ganglion and nerves were 

 exposed on both sides, but the connective tissue which surrounds 

 the nerves was left untouched because I feared that manipu- 

 lation might injure them. 



For the study of the cells, the ganglion with its nerve was fixed 

 in Bouin's fluid for twenty-four hours according to the procedure 

 described by Sugita ('17). Then the materials were washed 

 for twenty-four hours in running water, run through the alcohols, 

 cleared in xylol, rapidly imbedded in paraffin, cut in sections 

 8 M thick in the horizontal plane, stained with a 1 per cent solu- 

 tion of carbol-thionine, and mounted in acid-free balsam. 



To improve the staining I left the sections for ten minutes in 

 an aqueous solution of lithium carbonate before they were put 

 in the thionine. 



For the study of the nerve fibers the three branches and the 

 fifth (Vth) nerve were removed close to the ganglion and some- 

 times with the ganglion. In the case of very young rats — four 

 to eight days old — the ganglion and all its nerves were fixed 

 entire. To prevent distortion the nerves were extended to their 

 normal length on a bit of cardboard and then fixed in a 1 per 

 cent solution of osmic acid for five days. They were then washed 

 for twenty-four hours in water and finally were passed through 

 the alcohols, imbedded, cut in cross-section at 6 n, and the sec- 

 tions mounted as usual. 



The measurement of the ganglion cells was made with a Zeiss 

 microscope in which each division of the micrometer eyepiece 

 equaled 4.47 fx. Twenty-five of the largest cells in each ganglion, 

 namely, five cells from each of five sections, which were chosen 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 32, NO. 2 



