GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXXI 



of the wax will always be removed with the section, and 

 must be detached from the knife by the aid of a little turpen- 

 tine ; the preparation will then float off, and may be placed 

 upon the slide, or in a little cell, without further trouble. 



If the preparation is to be subjected to no further manipula- 

 tion, it is floated on to the centre of a slide, the superabundant 

 fluid removed with care, and a drop of Canada balsam applied, 

 after which a cover is placed upon it. The preparation is by 

 this means completely preserved, and can be kept in this state 

 and fit for examination for years. The process of imbedding 

 in gum requires greater attention to minutiae ; but it is appro- 

 priate for specimens which contain much connective tissue, and 

 answers for them much better than imbedding in wax. The 

 preparation need not be impregnated with oil. It may be 

 macerated for twenty-four hours in alcohol, of ordinary 

 strength, and from thence be removed into a paper cone filled 

 with a very concentrated solution of gum; the whole cone 

 must then be immersed again in alcohol. In the course of 

 two or three days the gum acquires a consistence which 

 renders it very fit for making sections. No definite statement 

 can be made in regard to the degree of this consistence, since it 

 must be proportionate to the hardness of the tissue. Better 

 sections are made of very soft tissues when they are imbedded 

 in a mass which is not too hard, and vice versa. The sections may 

 be floated off by means of a little water, and be examined after 

 the addition of a drop of glycerine ; or they may be subjected 

 to further manipulation. In the former case, if it be desired to 

 preserve the preparation permanently, the excess of glycerine 

 is to be removed from the edges of the cover, and these may 

 then be painted with a layer of varnish, which hardens on 

 exposure to the air. For this purpose a solution of asphalt 

 in turpentine, the so-called asphalt varnish, or some similar 

 material, may be employed. The preservation of preparations 

 in glycerine exerts no prejudicial influence upon them, and 

 when it can be used it is preferable to Canada balsam. Sections 

 which have been taken out of water may, however, be placed 

 in alcohol, then in oil of cloves, and from thence they may be 

 removed to Canada balsam, in which they may be preserved. 

 The contours of morphological elements, not previously 



