108 METHODS. 



nective tissue rna3 r be temporarily mounted in glycerin, but 

 cannot be preserved for a length of time in that liquid. 



All sections which are intended to be permanent, excepting 

 those of tissues prepared by the gold or silver methods, must 

 be mounted in Canada balsam or Dammar ; the last being 

 preferable, as more easy to manipulate. It is prepared as 

 follows: 



Preparation of Dammar Varnish. Half an ounce of 

 gum Dammar in powder, is dissolved in an ounce and a half 

 or two ounces of turpentine, and half an ounce of gum mastic 

 in two ounces of chloroform. The two solutions are then 

 separately filtered and mixed. This varnish so obtained is 

 clear, and if exposed in a thin layer on a plate of glass solidi- 

 fies rapidly. The sections which are to be mounted must be 

 placed, for a quarter of an hour or more, in a capsule contain- 

 ing absolute alcohol, which should be provided with a cover. 

 Each section must be raised with the aid of a german-silver 

 or copper lifter (the blade of which is then placed on blotting- 

 paper, to remove the adhering alcohol), and transferred to a 

 watch-glass containing oil of cloves. By this means it be- 

 comes, in a few seconds, quite transparent. If it is colored, 

 the color becomes more intense; if it is unstained, it becomes 

 almost invisible. From the oil of cloves it is transferred by 

 the same means to a drop of Dammar varnish, previously 

 placed in the centre of an object-glass. 1 



If excessively delicate and thin sections are to be mounted, 

 such, e. g., as sections of the retina, or of any thin membrane, 

 it is not possible, without risk, to transfer them from one 

 liquid to another. In this case it is, therefore, necessary to 

 swim the section directly from the knife on to the object-glass, 

 in which position they must be treated with the several liquids 

 to be employed ; and each liquid must be allowed to fall on 

 to the section, and, after producing its effect, removed by in- 

 clining the glass, care being taken not to allow the object to 

 float away at the same time. All delicate sections must be 

 protected by the interposition, between the object and cover- 

 glass, of a square of silver paper, with a window cut in it 

 somewhat smaller than the latter. 



Methods of Preserving Preparations permanently. 

 Preparations which are to be preserved must be mounted 



1 The lifter or spoon may be made by flattening the end of a copper 

 or german-silver wire, and bending it at right angles. It is desirable 

 to place the object-glass on a white ground if the object is stained, or 

 on a black ground if it is unstained, in order that the folds, if present, 

 may be seen and removed. If several sections are to be placed under 

 one cover-glass, each section may be pressed gently down on the sur- 

 face of the glass before covering ; the sections then adhere to the glass 

 sufficiently to keep in their places. 



