OF MICROSCOPIC OBJECTS. 57 



cell or wall is upon the slide, this is quite necessary, 

 otherwise the varnish will be most certain to extend, as 

 before mentioned, and ruin the object. It may be stated 

 here that gold-size differs greatly in its drying powers, 

 according to its age, mode of preparation, &c. (Chapter V.) : 

 here gum dammar solution laid on in a very thin coating 

 will be found most useful, as it dries so rapidly that it cannot 

 run in unless laid on with an unsparing hand. 



Should any object be enclosed which requires to be kept 

 flat during the drying of the cement, it will be necessary to 

 use some of the contrivances mentioned in Chapter II. 



When the slide is thus far advanced, there remains the 

 finishing only. Should the student, however, have no 

 time to complete his work at once, he may safely leave it at 

 this stage until he have a number of slides which he may 

 finish at the same time. There are different methods of 

 doing this, some of which may be here described. 



If ornamental papers are preferred, a small circle must 

 be cut out from the centre a little less than the thin glass 

 which covers the object. Another piece of coloured paper 

 is made of the same size, and a similar circle taken from its 

 centre also, or both may be cut at the same time. The 

 slide is then covered round the edges with paper of any 

 piain colour, so that it may extend about one-eighth of an 

 inch over the glass on every side. The ornamental paper 

 is then pasted on the " object " surface of the glass, so that 

 the circle shows the object as nearly in the centre as possible, 

 and covers the edges of the thin glass. The other coloured 

 paper is then affixed underneath with the circle coinciding 

 with that above. And here I may observe, that when this 

 method is used there is no necessity for the edges of the 

 slide to be ground, as all danger of scratching, &c., is 

 obviated by the paper cover. 



Many now use paper covers, about one and a half inch 

 long, on the upper side of the slide only, with the centre 

 cut out as before, with no other purpose than that of 

 hiding the edge of the thin glass where it is united to the slide. 



