134« UNPRESSED MOUNTING FOR MICROSCOPE. 



than Canada Balsam or Dammar, we proceed thus : — The top 

 edge of the cell we cover with a thin layer of brown cement ; 

 then we breathe into the cell, and before the moisture dries fill it 

 up with the solution for mounting in. If we did not breathe into 

 the cell, there would probably be an ugly rim of minute air- 

 bubbles clinging round its bottom angle. Into the cell we now 

 place our Blow-fly's head or other object, and with a needle or 

 small sable-brush arrange it in the centre in any desired position. 

 Insects mount best by placing them on their backs. 



After seeing that the cell is brimful with fluid, we take up a 

 clean cover-glass of such a size that it is not quite so wide as the 

 full width of the vulcanite ring, and on the under side of this we 

 breathe gently : then quickly place one edge downwards on to the 

 vulcanite ring, in the position it vrill finally occupy, and somewhat 

 slowly lower down the opposite edge on to the ring till the cover- 

 glass lies flat. If this is properly done, there will be no air- 

 bubbles in the cell, nor any clinging to the cover-glass ; neither 

 will the object be forced from its central position. To ensure the 

 still tacky cement fastening the cover-glass securely, we place over 

 the whole a slight spring-clip, and leave the mount thus for some 

 hours. Then the clip may be taken off, and the slide washed 

 under t*he tap ; when dry, a new ring of cement should be placed 

 on the edge of the cover-glass and on the outer edge of the 

 vulcanite ring : to which any rings of coloured cement may 

 afterwards be added. There are few finishing cements that are 

 equal in appearance, or so durable, as that made by adding one- 

 third of gold-size to some Brunswick Black : it dries rapidly and 

 is tough and elastic. 



For mounting in Canada Balsam or Dammar, we make a 

 similar ring of brown cement on the vulcanite ring. Inside the 

 ring, or cell, we place a drop or two of turpentine, which we then 

 shake out again, and fill up the cell with the fluid balsam. Into 

 this we place the object, taking it from the turpentine in which it 

 had been left to soak, and arranging it in the cell. On the under- 

 surface of a clean cover-glass we place another drop of turpentine, 

 allow it to run off, and then lower down the cover-glass just as in 

 the former case. After the spring-clip has been on for a day or 

 two, we can carefully scrape off the excess of balsam, wiping the 

 top carefully with a rag moistened in spirit, and then running a 

 ring of cement round the edge as before. 



And now we have mounted, let us say, two heads of the Blow- 

 fly, — one in glycerine fluid, the other in Canada Balsam. Let us 

 see how they look through the microscope. Our first impression 

 is — how different the object appears to that spread-eagle thing we 

 have so often looked at ! Why, we can actually focus down and 



