WITH THE MICROSCOPE. 20Q 



Accidents of this kind can always be avoided, by not allowing the drop 

 of the reagent to touch the deposit until the rod has been removed. 

 The drop may be placed near the substance intended for examina- 

 tion, and then allowed to come into contact with it, either by 

 inclining the glass slide, or by leading it with a glass rod, to the 

 matter to be tested. 



3O7. Bottles with Cayillary Orifices. The above tests may be 

 preserved in ordinary stoppered bottles, but I much prefer to keep 

 them in small tubes with capillary orifices, from which only a drop, 

 or a part of a drop, can be expelled when required. Several years 

 since I arranged all the ordinary tests I required for microscopical 

 purposes in small bulbs which were drawn off to a capillary point 

 They were provided with glass and gutta percha caps. These bulbs, 

 however, were somewhat inconvenient in consequence of not being 

 made to stand upright, and Mr. Highley substituted for them tubes 

 with flat bottoms and ground glass caps, pi. XLV, figs, 278 to 281. 

 To fill these bottles I proceed as follows : A little of the solution 

 is poured into a small basin, the tube being inverted so that its 

 orifice dips beneath the surface of the fluid. Heat being now applied 

 to the body of the bulb, the air in its interior is expanded and par- 

 tially expelled. As the bottle becomes cool, a certain quantity of 

 the fluid rises up into its interior. Usually, however, it is not pos- 

 sible to introduce more than a few drops in this manner. The bottle 

 is then removed and heated over the spirit-lamp until the drop of 

 fluid in its interior is in a state of ebullition. While the steam is 

 issuing violently from the orifice, I carefully plunge it again beneath 

 the surface of the fluid. As the steam within condenses, the solution 

 rises up in the interior, and would completely fill the little bottle if 

 it were maintained in this position, but when it is about three parts 

 full it may be removed from the fluid. If I were to fill it completely 

 it would be difficult to expel the fluid when required. A certain 

 quantity of air, therefore, is allowed to remain within the bottle, and 

 being expanded by the warmth of the hand, the quantity of fluid 

 required can be driven out at pleasure. 



Mr. Highley has made a further modification by arranging the 

 capillary neck in the form of a tubulated stopper, by the removal of 

 which, fluid can be introduced as in filling an ordinary bottle, 

 fig. 280. For microscopical purposes bottles with capillary orifices 

 possess many advantages over the ordinary stoppered bottles in 

 which tests are usually kept. 



In the first place, a most minute quantity of the test can be 

 obtained without difficulty, and there is no chance of too much 

 escaping. 



p 



