l32 UNPEESSED MOUNTING FOR MICROSCOPE. 



which answers a double purpose ;— it enters readily the very 

 minutest passages, displacing the contained air, and it also 

 dissolves the globules of fat left unsaponified by the soda- 

 solution. After leaving the ether for fifteen minutes in the corked 

 tube, and shaking it once or twice, we pour it off and add tur- 

 pentine; and then in ten minutes' time our blow-fly's head is 

 ready for mounting in Canada Balsam or Dammar. 



But if so mounted, it will be very difficult to see much of the 

 finer internal structure, since these media render some parts far 

 too transparent : and hence some of the glycerine media are 

 preferable. In such cases, after pouring off the ether add alcohol, 

 and at the end of fifteen minutes replace the alcohol with cold 

 water, and leave for fifteen minutes more. Then the water may be 

 poured off, and the mounting-fluid, whether glycerine, carbolic- 

 acid, gelatine, Goadby's or Thwaites' fluid, may be added. The 

 object, if mounted in any of these, will have a far more natural 

 appearance, and show more plainly the finer structures, than if 

 mounted in Canada Balsam. The times mentioned above are 

 those it is fiecessary in most cases to wait, but longer intervals 

 would often be preferable. If we are busy, the tube and its con- 

 tents may be left at any stage of the proceedings for days, with a 

 certainty that the object will only benefit by the delay; except in 

 the case of the soda-solution. Of course, when the object is 

 transparent enough, a longer stay in that solution would only 

 render it too transparent, and so spoil it. It is not necessary to 

 use distilled water, though it is better to do so ; but whatever 

 water is used, it should have been just freshly boiled and be used 

 hot. Cold, unboiled water contains a large quantity of air, and if 

 used in that state will certainly impart air to the object instead of 

 helping to extract it. 



The soda or potash solution is made by adding solid potash or 

 soda to eight times its weight of boiling water. 



The spirit and the etlier, which have been used during the 

 process, should be poured off into a separate waste bottle, either 

 to be afterwards redistilled, or for use in some other way : — ether, 

 being highly inflammable, should not be brought near a light. 

 The only expenses are for soda, alcohol, ether, and one tube ; 

 of the alcohol and ether there is practically very little waste, as a 

 pint of each will prepare some thousands of specimens. 



So far, we have written as if it were only the blow-fly's head that 

 we wished to prepare; but it is obvious that in the same tube we may 

 have some dozen or more insects, or parts of insects, — only being 

 careful to remember which is which. The same system will 

 answer likewise for plant specimens, such as sections of wood, 

 small seed-vessels, leaves, etc. Only in their case they should first 



