for Microscopical Examination. 265 



embedding mixtures, or in the gum mass cold, under the receiver of 

 an air-pump, and exhausted till bubbles cease to come from the 

 tissue, the mass will penetrate into the spaces, previously occupied 

 by air ; after solidification has taken place they may be dealt with as 

 an ordinary embedding, and in this way it will be possible to obtain 

 fine preparations. 



Professor Quekett used to inject hot tallow through the 

 bronchi into the air cells of an injected lung, which after cooling 

 and drying yielded a splendid mass. All transparent lung injec- 

 tions put up by Mr. Topping are prepared in this way ; although 

 this plan answers the purpose very well, it is doubtful if it be even 

 equal to the last. 



For making sections of the tissues thus embedded, razors or 

 section knives are used. I have employed for a considerable time 

 the flexible-edged, concave-sided razors made by John Heiffor, and 

 stamped " made for the army " ; they are extremely thin for some 

 distance from the edge, and the hollowed-out surface holds plenty of 

 alcohol ; this is absolutely necessary to prevent the section sticking 

 to the blade. Mr. Moseley* also strongly recommends them for 

 histological work. Dr. Klein's section knife has one side flat, and 

 the other concave ; the blade is eight inches in length. The razors 

 previously referred to are equal and considerably cheaper, being 

 obtainable from any cutler for the small sum of one shilling each. 

 Previous to cutting the tissue embedded in any of the fatty masses, 

 the instrument must be wetted with ordinary spirit, or, still better, 

 absolute alcohol ; in which liquid the sections must be placed as 

 soon as made, to clean them from the surrounding material, after 

 which they are ready for staining. If embedded in gum or gelatine, 

 water or glycerine must be used to moisten the knife, and the sec- 

 tions cleaned in water. For lung injected with tallow, the razor 

 is kept wet with turpentine, in which fluid the sections must be 

 immersed ; the tallow will readily dissolve, and the sections may be 

 put up at once in Canada balsam, or solution of damma or balsam 

 in benzole. t 



(C.) It is often desirable to obtain sections of perfectly fresh tissue, 

 for the purpose of immediate examination, or perhaps for impregna- 

 tion with some metallic salt. It is obvious that no assistance can 

 be looked for from hardening fluids or embedding, and very little 

 indeed by means of the double- bladed knife. We must have recourse 

 to one of the refrigerating methods. (1.) The process generally 

 adopted is that described by Klein in the 'Handbook for the 

 Physiological Laboratory,' from which the following is quoted : — 

 " A freezing mixture is prepared by introducing alternately small 

 quantities of broken ice, or snow (not so advantageous), and of 



* Moseley, foe. cit. 



t Bastiau, p. 96, No. 2, ' Monthly Microscopical Journal.' 



