102 METHODS. 



Methods by which Tissues are Hardened for the 

 Preparation of Sections. For the purpose of rapidly 

 hardening tissues, small portions may be advantageously 

 placed in the chloride of gold, osmic acid, or chloride of pal- 

 ladium, and kept till they are sufficiently consistent. Such 

 preparations must usually be embedded in the manner to be 

 hereafter described, before sections are made from them. The 

 sections themselves are then exposed to the light in distilled 

 water, and covered in glycerin. Half per cent, solution of 

 chloride of gold, solutions of perosmic acid varying from one- 

 tenth to two per cent., or solutions of chloride of palladium 

 from one-tenth to half per cent., are used. 



Other agents and methods in use are the following : Alco- 

 hol, oxalic acid, boiling and drying, chromic acid and its com- 

 pounds, (a) For thin membranous tissues, hardening in alco- 

 hol answers well. It is more rapid than chromic acid, which, 

 however, has superseded it for many purposes for which it 

 was formerly employed. Absolute alcohol is used principally 

 for hardening brain, and for injected tissues. Common alco- 

 hol is also used for the hardening of pancreas, salivary glands, 

 and the glands of the stomach and intestine, and of objects 

 which have been already treated with gold or silver. Further, 

 when tissues have been partly hardened in chromic acid com- 

 pounds, the hardening can be accelerated and completed by 

 subsequent immersion in common alcohol. (6) The use of 

 oxalic acid and oxalates, and other similar salts, may be en- 

 tirely dispensed with. If used, weak solutions of from a half 

 to two per cent, are preferable, (c) The process of boiling, 

 etc., is entirely relinquished. In former times it was employed 

 for intestine, kidney, trachea, and larynx. The intestine was' 

 boiled in a mixture of water, creasote, and vinegar, stretched 

 on cork, and dried. Sections were made with scalpels, and 

 then steeped in acetic acid, (d) The chromium compounds 

 are the most valuable agents we possess for hardening viz., 

 chromic acid, in solutions varying in strength from one-tenth 

 to half per cent.; bichromate of potash, in solutions from half 

 to two per cent., and Miill r's liquid, which consists of two 

 parts of bichromate, and one part of sulphate of soda, in 100 

 parts of water. These have the immense advantage that they 

 produce no marked shrinking or distortion of the tissues, so 

 that they retain for the most part their natural characters. 

 This is particularly the case as regards bichromate of potash 

 and Muller's liquid. Yery small portions of tissue must be 

 used, particularly when chromic acid is employed, for it pene- 

 trates much less readily into the tissues than the others ; so 

 that if the preparation is too large, it is apt tq become putrid 

 in the centre, while the outside is too hard. If the objects- 

 are smeared with foreign matters, as, e. g., intestine by intes- 



