OP MICROSCOPIC OBJECTS. 101 



rubbing down needles upon a hone. They are more pleasant 

 to work with when short, as the spring they have whilst 

 long robs them of much of their firmness. Glass points 

 made by drawing out glass rods to a point will be found 

 useful in manipulating with acids. 



A glass syringe is also useful in many operations, serving 

 not only to cleanse the objects but to add to, or withdraw 

 liquids from, the dissecting -trough. This trough wiU now be 

 described, as many substances are so changed by becoming 

 dry that it is impossible to dissect them unless they are 

 immersed in water during the operation. If the object be 

 opaque and must be worked by reflected light, a small square 

 trough may be made to the required size, of gutta-percha, 

 which substance will not injure the edge of the knives, &c. ; 

 but where transparency is necessary, a piece of thin plate- 

 glass must be taken, and by the aid of marine-glue (as 

 explained in Chapter Y.) sides affixed of the required 

 depth. As pins, Ac., cannot be used with the glass troughs 

 and the substance must be kept extended, a thin sheet of 

 cork loaded with lead in order to keep it under water may 

 be used ; but this, of course, renders the bottom opaque. 

 When working with many thin substances, a plate of glass 

 three or four inches long and two wide will serve every 

 purpose, and be more pleasant to use than the trough. A 

 drop or two of water will be as much liquid as is needed, 

 and this will lie very well upon the flat surface. As these 

 are the principal apparatus and arrangements which are 

 requisite in dissection, the method of proceeding in a few 

 cases may now be noticed. 



VEGETABLES. The dissection of vegetable matter is much 

 less complicated than that of animal ; maceration in water 

 being a great assistant, and in many cases removing all 

 necessity for the use of the knife, especially if hot water can 

 be used without injury to the objects, as is the case with 

 many. This maceration may be assisted by needles, and 

 portions of the matter which are not required may be re- 

 moved by them. When, for instance, the spiral vessels 



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