APPENDIX. 



mould and specimen should be filled with cold water until the latter 

 is just on the point of overflowing the sides of the mould, great care 

 being taken that this does not happen before the surface of the enclosed 

 lake of melted paraffin has congealed, otherwise the paraffin becomes 

 partially displaced by the water, which will be found later within large 

 cavities in the block. 



As soon as the film on the.surface has completely formed, the water 

 is allowed to cover the mould entirely ; the dish may then be placed 

 under the tap, and a gentle stream of water aid in cooling off the 

 mass. No attempt should be made to remove the block from the 

 mould until the entire mass has become thoroughly hardened when 

 this has occurred, and the embedded object with its surrounding mass 

 has been freed, the paraffin should appear almost transparent and 

 of a bluish tint, and not milk-white, as is usually the case when the 

 paraffin is impure or when the block has been cooled slowly. After 

 trimming off the superfluous embedding material and exposing the 

 surface to be sectioned, the tissue is ready for cutting. Objects may 

 be preserved within the paraffin indefinitely, the method affording an 

 admirable and convenient means of keeping tissues for any length of 

 time and always ready for immediate sectioning and mounting. 



Celloidin Method {Duval-Schiefferdecker). 



This method has but one point in common with the paraffin process 

 the tissue is infiltrated with the embedding mass ; while paraffin is 

 cut dry, celloidin must be cut under or flooded with spirit. Celloidin 

 is particularly adapted for certain lines of work in the central nervous 

 system and the special senses, and possesses the advantages over 

 paraffin of requiring less attention and no heat for its successful manip- 

 ulation. The retention of the supporting mass, the rather thicker 

 sections, and the impossibility of cutting ribbon-series, on the other 

 hand, are points of unfavorable comparison with the paraffin method. 



The celloidin should be prepared as two solutions, a thin and a 

 thick: the celloidin either as chips or in cake is dissolved in equal 

 parts of absolute alcohol and ether, about 5 grammes, in small pieces, 

 being placed in 100 c.c. of the mixed solvent ; the resulting solution 

 will be very thin, and may be labelled "A" ; a second solution should 

 be made containing enough celloidin to secure the consistence of a 

 thick syrup; this is "B." The celloidin does not dissolve with 

 great readiness, days often being required for the preparation of the 

 solutions ; these should be very carefully guarded against evapora- 

 tion, and a small quantity of the absolute alcohol and ether added 

 from time to time to maintain the proper degree of fluidity. 



The tissue, previously thoroughly dehydrated by absolute alcohol, 

 is soaked in a mixture of equal parts of absolute alcohol and ether 



27 



