116 Dr. Griffitli on preservinff Microscopic Objects, 



as to avoid the risk of its being broken. The base is now wiped per- 

 fectly dry and clean, the object laid on its centre ; a small quantity 

 of the preservative liquid is next dropped on it ; upon this is laid the 

 thin glass square, wiped perfectly clean : should the quantity of li- 

 quid added be not sufficient to fill the whole space between the two 

 glasses, a little more must be added* until such is the case ; if too 

 much has been added, it may be readily removed by a fine pipette, 

 camel-hair pencil, or moistened piece of blotting paper. When the 

 surfaces of both glasses, not in apposition, are quite free from moist- 

 ure, some gold size thickened by intimate mixture with lamp-black 

 must be laid all round the edges of the thin glass, partly also upon 

 the contiguous portions of the lower, so as to hermetically inclose 

 the liquid and the object. The mixture of the finely-powdered lamp- 

 black and the gold size (the latter of which ought to be old) should 

 be about the consistency of treacle, or rather less. If made too thin, 

 it is apt to run in under the upper glass and destroy the specimen. 



When the objects are large, the following mode is generally adopted. 

 A circular depression is excavated in the substance of the basic slip, 

 which is double or treble the ordinary thickness, and in this the object 

 and the liquid are placed ; these are then covered with thin glass, and 

 the gold size and lamp-black applied as above around the edges of 

 the latter. Or a square piece of thick crown glass, less in size than 

 the breadth of the basic slip, has either a circular or square hole 

 drilled through it ; this is next fastened to the base either by Canada 

 balsam or varnish ; a cell is thus made in which the object and 

 liquid are placed ; the thin glass slip is next applied upon the upper 

 surface of the excavated piece ; it is then covered at the edge, and 

 rendered adherent to it by the gold size and lamp-black. 



Another method is this. Take a basic slip of glass, and spread a 

 little white lead ground up with oil (or painter's white paint) on its 

 upper surface, leaving an aperture in the middle to receive the object. 

 This requires to be painted over and over until it has become of the 

 thickness of the specimen to be preserved ; the blank space or cell is 

 next filled with one of the preservative liquids, and the object then 

 immersed in it ; a slip of thin glass is now laid upon the surface of 

 the white lead and rubbed close on to the paint, beginning at one 

 end and passing across the slide to the other, so as to force out any 

 air-bubbles. When dry the specimen is permanent. These will, I 

 think, be found sufficient for the preservation of almost any objects ; 

 there are, however, a few which it is very difficult to retain perfect. 

 Many I have preserved simply by leaving them to dry between two 

 slips of glass, without any preservative fluid or balsam. Blood-discs, 

 &c. have kept remarkably well in this manner ; but we can place no 

 dependence on so doing, for one which is good perhaps there are 

 twenty spoiled. Talc was formerly used instead of thin glass to cover 

 objects, but it is very objectionable on account of its being so readily 

 scratched, the difficulty of procuring it free from flaws, and its pe- 



* On the end of a camel-hair pencil or pen ; it will run n by capillary 

 attraction. 



