94 IMBEDDING METHODS. 



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 to 25 per cent, solution containing 8 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 mixture of 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. Sections 

 must be very gradually passed through 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 then be mounted in balsam. To mount in glycerin is of course 

 easy. 



BURZYNSKI (Polu. Arch. Biol. Med. Wiss., i, 1901, p. 39) finds 

 that alkaline formol hardens gelatin better than acid. 



GASKELL (Journ. Path. Bact., July, 1912, p. 58) soaks in pure 

 gelatin, melted s.a., for two to five hours at 37 C., and hardens the 

 mass in vapour of formol, for three or more days. To cut, he freezes. 

 He mounts in glycerin jelly, to avoid dehydration and shrinkage. 



