XXX INTRODUCTION. 



by the fingers, or possess a cavernous structure which it is 

 desirable to preserve, or if they present irregularities and pro- 

 jections of the surface, like villous processes, or papillse, and 

 sections of these are required, the best method of dealing with 

 the specimen is to imbed it. 



The process of imbedding consists in dipping the tissue into 

 some liquid which will easily set, even at the ordinary tem- 

 perature of the air. For this purpose we may employ, first, a 

 mixture of wax and oil, and secondly, a concentrated solution 

 of gum. The first is prepared by melting oil and wax, in 

 equal proportions, in a porcelain capsule, by the heat of a lamp. 

 The proportions of the two substances can, of course, be varied ; 

 and, according to the peculiarities of the case, whether it is re- 

 quired to be a little harder or softer, more wax or more oil must 

 be added. The piece of tissue which is to be imbedded should 

 first be kept in alcohol for a length of time sufficient to cause 

 it to be thoroughly impregnated with that fluid, or, perhaps 

 more correctly speaking, till the water it contains is as far as 

 possible removed. This will occupy a longer or shorter period, 

 in proportion to the strength of the alcohol; with absolute 

 alcohol, and with small pieces of tissue, a few minutes are 

 sufficient. The specimen is then to be placed in pure oil of 

 cloves, which is far preferable to the oil of turpentine, that 

 at one time was so generally used, partly on account of its 

 more agreeable smell, partly because it is not so volatile, and 

 partly also because it produces a consistence in the preparation 

 more favourable to the obtainment of firm sections. The spe- 

 cimen must remain in the oil of cloves till it is transparent, the 

 infiltration of the oil being incomplete so long as any opaque 

 spots remain visible. A little cone of paper may then be pre- 

 pared, which is to be filled with the mixture, and into this the 

 specimen is placed, whilst it is still fluid. Before the mass 

 cools, the position of the object should be noticed ; and when it 

 has become firm and opaque, its situation may be indicated 

 by a mark on the surface of the wax, through which, when per- 

 fectly cold and hard, the section can be carried. The section 

 must be floated off from the knife. Imbedding is best adapted 

 for very delicate objects, which have little consistency, and 

 which cannot well be seized with forceps or needles. A portion 



