for Microscopical Examination. 261 



and hydrochloric acids in a state of extreme dilution have been 

 recommended by Dr. Frey * and Dr. Beale. t 



Cartilage, whether hyaline or fibrous, needs no preparation. 

 Glandular, nervous, and muscular tissues, and other soft struc- 

 tures, require hardening in methylated alcohol, solution of 

 chromic acid and its salts, either singly or combined, or in union 

 with sulphate of soda, varying in strength from 2 to \ per cent., 

 or even less. Saturated aqueous solution of picric or carbazotic 

 acid, strongly recommended by KanvierjJ solutions of osmic acid, 

 £ per cent. (Schultze), bichloride of platinum (Merkel), bichloride 

 of mercury, and chloride of palladium (Schultze). Of all these, 

 chromic acid, its salts, and alcohol are preferable. It is not my 

 province to enter into the subject of softening and hardening, 

 suffice it to say that tissues may be made to assume — by subjecting 

 them to the action of these solutions — a sufficient degree of soft- 

 ness in the first case, or of solidity in the last, to permit of sections 

 being made with an ordinary razor or scalpel. For this purpose, a 

 piece of cartilage, or of any tissue which has been softened or 

 hardened to a density resembling it, may be held in the hand, or 

 placed on a small, flat, plate of wax, being fixed in a convenient 

 position by the middle finger and thumb of the left hand, whilst the 

 thickness of the section is regulated by the nail of the forefinger of 

 the same hand. The razor, which should be wetted with water, 

 spirit, or glycerine, in this case must be held horizontally, with the 

 cutting edge directed downwards ; the section is made by drawing 

 it from before, backwards. This method has been in use for some 

 time at the London Hospital, and is universally liked. 



For the purpose of hardening, the following agents may also be 

 employed : — Aqueous solution of oxalic acid ; drying, or boiling in 

 a mixture composed of creosote, vinegar and water, and then drying ; 

 but they cannot be recommended ; all have been deservedly superseded 

 by those previously enumerated, and are now entirely relinquished. 



III. We will now direct our attention to the preparation of 

 sections from those tissues classed in the third division, which 

 includes nearly all fresh material, from which good preparations 

 cannot be obtained, without the assistance of some special arrange- 

 ment, e. g. Valentine's knife, embedding, or freezing. 



(A.) The double-bladed knife invented by Professor Valentine is 



especially recommended by Dr. Beale.§ It has been made to assume 



an endless variety of forms, every maker of the instrument modifying 



it in some way. Four forms only are worthy of notice. (1.) The 



original consists of two blades, differing in length ; the longer is 



firmly secured in an ivory handle, the shorter is fixed to the longer 



* Frey, ' Das Mikroskop unci die Mikroskopische Tecknik,' American transla- 

 tion by Dr. Cutler. 



t Beale, ' How to Work with the Microscope.' 



% Frey, loc. cit. § Beale, Inc. cit. 



u 2 



