OF MICROSCOPIC OBJECTS. 107 



makes edged instruments by 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. 



A glass syringe is also useful in many operations, serving not 

 only to cleanse the objects but to add or withdraw liquids from 

 the dissecting-trough. This trough will 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 is opaque and must be worked by reflect- 

 ed 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 ex- 

 plained in Chapter IV.) the sides affixed of the required depth. 

 As pins, &c., cannot be used with the glass troughs and the sub- 

 stance 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. This maceration may be assisted by needles, and 

 portions of the matter which are not required may be removed by 

 them. When, for instance, the spiral vessels which are found in 

 rhubarb are wanted, some parts containing these are chosen and 

 left in a small quantity of water until the mass becomes soft, and 

 this is more quickly effected when the water is not changed. The 

 mass must be then placed upon a glass plate when practicable, or 

 in the trough when large, and with the aid of two needles the 

 matter may be removed from the spiral vessels, which are plainly 

 seen with a comparatively low power ; and by conveying these 



