194: THE MICROSCOPE AND ITS REVELATIONS. 



halves attached at one end, but made to .diverge a t the other at any 

 angle, being there fixed by a clamping screw. l 



SECTION 2. Preparation and Mounting of Objects. 



189. Imbedding Processes. The preparation of soft Organic sub- 

 stances for Section-cutting by ' imbedding/ may be made in. two modes, 

 the choice between which will depend upon the consistence of the sub- 

 stance. If (1) it be compact, like a piece of liver or kidney, it only 

 needs to be surrounded by the imbedding mass, which will afford it as a 

 whole the requisite support. But if (2) it be partly, occupied, like a piece 

 of lung, by interstitial cavities, it must be penetrated by the imbedding 

 substance, so that every part may be duly supported. For simple im- 

 ' bedding, nothing is so suitable as the firmer fats; which must not, how- 

 ever, be so hard as to be brittle. Thus, if white Wax be used, it should 

 be melted with an equal weight of olive oil; if Paraffine or Spermaceti, it 

 should be melted with about one-fifth of its weight of lard or soft tallow. 

 The latter is generally to be preferred, as shrinking less in cooling; the 

 cylinder formed by the hardened wax being liable to become loose in the 

 well of the Microtone. Either mixture being kept in stock, carefully 

 secluded from dust, a small quantity of it should be melted for use in a 

 porcelain basin floated in a water-bath. To avoid injury to the tissue, 

 its temperature should not be raised more than is requisite for its thor- 

 ough liquefaction. The substance to be cut, having been previously 

 hardened ( 199), should be taken out of the spirit in which it is pre- 

 served; and a piece of suitable size having been cut off, this should bo 

 placed on blotting-paper, so that the spirit may drain away, and its sur- 

 face may become dry. It is then to be dipped (as recommended by Dr, 

 Sylvester Marsh), in a very weak solution 20 grains to the ounce of 

 Gum Arabic, care being taken in doing so not to squeeze out the spirit so 

 as to remoisten the surface; and the superfluous liquid being then again 

 removed by blotting-paper, the surface will in a few minutes become dry 

 and glazed with a thin film of gum, the use of which is to keep the 

 imbedding substance from adhering to it. The plug of the Microtome 

 (which may advantageously have a large-headed screw inserted into its 

 upper side, to furnish a ( hold ' for the imbedding substance) being set 

 at the depth of about an inch beneath the cutting-bed, melted wax or 

 paraffine is to be poured into it to about half this depth; and the sub- 

 stance to be cut being then held in the tube in the best position (which 

 is not its centre, but nearer the side next the operator), the imbedding 

 material is to be slowly poured in, until the imbedded substance is 

 entirely covered, and the cavity completely filled. When the imbedding 

 material has become quite solidified by cooling, the cutting of sections 

 may be proceeded with. 



190. When, however, it is necessary that the substance to be cut 

 should be entirely penetrated by the imbedding material, a much longer 

 preparatory process is necessary. In many cases in which the sections 

 are required to display rather the general than the minute structure, 

 satisfactory results may be obtained by keeping the substance (previously 

 steeped in pure water) immersed for a lengthened period at a gentle 

 warmth, either in a strong mucilage of Gum Arabic, or in a solution of 

 Gelatine that will 'set' on cooling, its cavities having been laid open 



Brandt in " Zeitschrift fur Mikrosk.," Bd. ii. (1880), p. 172. 



