OF MICROSCOPIC OBJECTS. 163 
rubbing down needles upon ahone. 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 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 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 V.) sides affixed of the required 
depth. As pins, &c., 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. 
V2EGETABLES.—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 
M 
