Smith, on a Dissecting Microscope. 13 



found necessary, an advantage too obvious in many instances 

 to need further comment. As pieces of glass of several widths 

 would be required to suit objects of different sizes, thus ne- 

 cessitating the employment of several troughs fitted up in 

 this manner, it has occurred to me, that in case this might 

 form a ground of objection with some to the plan, the 

 same purpose might be answered by simply fitting slips 

 of glass of the sizes most generally useful into flat pieces of 

 gutta percha, which would go into any of the ordinary glass- 

 bottomed troughs, and thus easily be substituted the one for 

 the other. 



No. 3. 



=-^ 



It now only remains for me to notice the arrangement 

 figured in the above drawing, which shows a sectional view of 

 the stage of the microscope, under which is held, by two 

 catches, a large trough, about an inch and a half in depth, 

 and having a glass bottom ; a piece of sufficient size is also 

 cut out of the stage, and a moveable plate of glass, or metal, 

 put in its place (as shown in the drawing) , which is of course 

 lifted off when the trough is used ; another, and perhaps 

 more effectual, way of getting at it would be, by making a 

 portion of the stage nearly equal in length and breadth to 

 the trough to slide in a groove, like the lid of a small box, 

 which could just be pulled out when required. By this method, 

 I think that many dissections, that in the ordinary way would 

 be carried on apart from the microscope, might be made on 

 it ; thus allowing the hand-rests, mirror, condenser, and other 

 appurtenances of the instrument, to be made use of more 

 advantageously and with greater ease to the dissector than if 

 a trough of this size were placed on the top of the stage. In 

 order to make this arrangement as complete as possible, I 

 further propose to fit a piece of gutta percha into the bottom 

 of the trough, which could be taken out when wanted (and 

 thus make it serve the place of two troughs) ; and also to make 

 a small hole in it (fitted with a plug), so as to allow of the 

 water being drained off when necessary into a vessel held 

 below, without having to remove, or otherwise disturb the 

 object under dissection in any way, which might thus, if 



