GROWTH OF THE CEREBRAL CORTEX 521 



The method oj procedure 



The rat was chloroformed and its sex, body and tail lengths 

 and body weight recorded. After complete evisceration, the 

 brain was exposed and the pia mater carefully removed from 

 the surface of the brain. Then the entire brain was severed 

 from the cord by a transverse section at the level of the calamus 

 scriptorius and taken out, care being taken to preserve the para- 

 flocculi and the olfactory bulbs. The brain was put on a glass 

 plate, basal surface down and without lateral support. The five 

 diameters of the hemispheres were next measured — according to 

 the method described in the first paper of this series (Sugita, 

 '17) — this procedure being desirable not only for the present 

 study but also for a study on the changes in the size and shape 

 of the brain according to age. The total brain was then put 

 into a closed weighing bottle and weighed to the tenth of milli- 

 gram. The brain was next transferred to Bouin's fluid for 24 

 hours at the room temperature, the basal surface of the brain 

 being in even contact with the bottom of the vessel. After 

 fixation, the brain was washed with running water for 20 min- 

 utes and then put into 20 cc. of 80 per cent alcohol for 24 hours 

 and into 20 cc. of 90 per cent alcohol for 24 hours successively, 

 for dehydration and further fixation. On the occasion of each 

 change of fluid the diameters of the hemispheres were measured 

 and the total weight taken in order to record the modifications 

 produced. 



With india ink and a fine brush lines were circumscribed on 

 the surface of the brain in order to designate the planes from 

 which sections should be taken after imbedding. The positions 

 of these lines will be described in the following chapter. Slices 

 about 2 mm. in thickness and including the level from which 

 the sections were to be taken, were made, and placed in 10 cc. of 

 absolute alcohol for 6 hours, then in xylol for one and a half 

 hours at the room temperature, transferred into the xylol-para- 

 fine mixture for one and a half hours in the oven at 37°C., and 

 finally imbedded in parafiine for two hours at about 56°C. I 

 have used the paraffine with the melting point at 54°C. in winter 



