178 WILLIAM F. ALLEN 



it was impossible to destroy the sensor}^ trigeminal root without 

 destroying the motor root also, which of course produced a com- 

 plete paralysis of the masticator muscles of the left side, so that 

 it was necessary to nurse the animal for several days after the 

 operation. The food selected was a saturated solution of cane- 

 sugar in milk, which was administered through a pipette. In 

 most cases a guinea-pig would regain the use of its jaws suffi- 

 ciently to chew lettuce in a few days after the operation. 



Microscopical technique. The animals were killed fourteen or 

 fifteen days after the operation and the brains, including the 

 trigeminal roots, were carefully removed and placed for a day or 

 two in a 3 per cent potassium bichromate solution. Most of the 

 cerebellum and the cerebral hemispheres were cut away from 

 each brain, care being taken not to injure the remaining struc- 

 tures. The brain stem was then cut into three pieces, measured 

 off so that the middle piece contained the trigeminal roots intact 

 and extended cephalad to include most of the superior coUiculus. 

 The material was then changed to a fresh 3 per cent solution of 

 potassium bichromate, where it remained for a period of three 

 weeks. After rinsing with w^ter, it was placed for thi-ee weeks 

 in the following solution: 1 per cent osmic acid, 10 cc. ; 3 per cent 

 potassium bichromate, 30 cc. After this it was washed for 

 twenty-four hours in nmning water; thoroughly dehydrated for 

 a day in each grade of alcohol from 70 per cent up to 100 per 

 cent; then to an alcohol-ether mixture for twenty-four hours, 

 thin collodion three days, chloroform one hour, benzol two 

 hours, benzol-soft paraffin twelve hours, medium (melting point 

 about oO°C.) paraffin three hours, embedded in medium paraffin, 

 cut into 20 n sections, mounted serially on slides with the egg 

 albumen method, cleared in xylol, damar, and cover-glass. Ac- 

 cording to my experience, there need be no haste with the dehy- 

 dration process or with passing the material through ether, ben- 

 zol, or xylol. After degenerated myelin is thoroughly black- 

 ened by osmic acid it is not affected by long exposure to 

 these reagents, and one may as well have good sections as poor 

 sections, as a result of a hurried infiltration process. For small 

 brain sections the writer prefers the double collodion-paraffin 



