6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



half of the 2 percent ether-alcohol celloidin was removed from each 

 tube, and an equal amount of 3 percent celloidin dissolved in clove 

 oil was added, after which the infiltration under heat in the pressure 

 cylinder was continued for another 24 hours. Following this second 

 period, the celloidin was gradually thickened by suspending a tiny 

 piece of parlodion in the upper part of the solution, after which the 

 pressure infiltration was carried on for another day. Such additions 

 of parlodion were made daily until the solution reached the proper 

 consistency for imbedding. 



Hardening of the celloidin blocks was accomplished by immersing 

 the open infiltration tubes in chloroform for several days. It was 

 important, however, that the contents of the tubes be thoroughly cooled 

 before the hardening was begun. After hardening was completed, 

 each tube was tapped with some hard object until its glass wall was 

 cracked in several places. The resulting pieces of glass were carefully 

 picked away from the celloidin, and the block was soaked in chloro- 

 form until it ceased to float. 



The completely hardened celloidin block was infiltrated in paraffin 

 preparatory to double imbedding. During this process the clove oil 

 in the celloidin matrix was partially replaced by paraffin, thereby 

 eliminating the possibility of the celloidin pulling out from its paraffin 

 coating during sectioning. 



Because of the tendency of the celloidin matrix to warp during 

 heating and drying, the following method for mounting the ribbons 

 was used. The surface of the slide was first swabbed with a thick 

 layer of albumen fixative. Good quality cigarette papers were cut in 

 half longitudinally, and each half was laid on a flat surface and 

 saturated with distilled water. The microtomed ribbon was cut into 

 strips of the desired length, and these were laid in reverse order on 

 the paper. More distilled water was then applied to the paper, and the 

 resulting surface tension aided in pulling the ribbons out until they 

 were fairly flat. Thereafter, the paper was lifted up with the sections 

 adhering to it, reversed, and laid ribbon-side down on the albumen- 

 smeared slide. The whole was immediately blotted with several thick- 

 nesses of filter paper, a finger being rolled over this paper from one 

 end of the slide to the other, thereby insuring direct contact between 

 the sections and the slide at all points. Sections mounted in this 

 manner were certain to be flat and therefore suitable for photographic 

 purposes. 



Again, because of the tendency of the celloidin to warp, no period 

 of drying was allowed following mounting. Instead, as soon as the 

 cigarette paper was pulled away, leaving the ribbon adhering to the 



