IMBEDDING METHODS (GELATIN). 



The mass is then hardened in spirit or bichromate of potash, 

 picric acid, or the like. No heat at all is required in this 

 process. 



149. NICOLAS'S Method (Bibliogr. Anat., Paris, 3 annee, 

 I 1896, p. 274; Zeit.f. wiss. Mik., xiii, 1896, p. 218). Pre- 

 parations are first soaked for one or two days in a 3 per cent, 

 to 4 per cent, aqueous solution of gelatin kept at 25 C., 

 then for the same time in a 10 per cent, solution, and then 

 [ for two or three days more in a 20 per cent, to 25 per cent, 

 solution containing 8 per cent, to 10 per cent, of glycerin 

 and kept at 35 C. They are then imbedded in some of the 

 same mass in paper trays, and as soon as the gelatin has set 

 are thrown into a 5 per cent, solution of formaldehyde 

 (formol 1 part, water 7). After a few days therein the 

 gelatin has become hard and insoluble, and may be cut or 

 preserved for months in weak formol solution, or dilute 

 alcohol or glycerin, or even in pure water. The mass cuts 

 like celloidin, but unfortunately takes stains strongly. The 

 sections must be very carefully and gradually passed through 

 the successive alcohols for dehydration, as they curl up very 

 easily. They, however, flatten out at once on being brought 

 from absolute alcohol into cresylol, and may thence be 

 mounted in balsam. To mount in glycerin is of course easy. 



