PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 189 



others never succeed in attaining. The making of hand-sections will be 

 greatly facilitated by the previous use of the hardening and imbedding 

 processes to be hereafter described ( 189, 199); but the best of them 

 rarely equal good sections cut by a Microtome. For the preliminary 

 examination of any soft structure, such a pair of Scissors as is represented 

 in Fig 132 will often be found very useful; since, owing to the cur- 

 vature of the blades, the two extremities of a section taken from a flat 

 surface will generally be found to thin away, although the middle of it may 

 be too thick to exhibit any structure. The two-bladed Knife contrived 

 by Prof. Valentin was formerly much used for cutting microscopic sec- 

 tions of soft tissues: but as such sections can be cut far more effectively 

 by the methods to be presently described, a mere mention of this instru- 

 ment will here suffice. 



184. Microtome. There is a large class of substances, of moderate hard- 

 ness, both Animal and Vegetable, of which extremely thin and uniform 

 slices can be made by a sharp-cutting instrument, if they be properly held 

 and supported, and the thickness of the section be regulated by a mechan- 

 ical contrivance; such are, in particular, the Stems and Roots of Plants, 

 and the Horns, Hoofs, Cartilages, and similarly firm structures of Animals. 

 Various costly machines have been devised for this purpose, some of 

 them characterized by great ingenuity of contrivance and beauty of work- 

 manship, but most of the purposes 

 to which these are adapted will be FIG. 1,3. 



found to be answered by a very simple 

 and inexpensive little instrument, 

 which may either be held in the hand, 

 or (as is preferable) may be firmly 

 attached by means of a T-shaped piece 

 of wood (Fig. 133), to the end of a 

 table or work-bench. This instrument 

 essentially consists of an upright hol- 

 low cylinder of brass, with a kind of 

 piston which is pushed from below 

 upwards by a fine-threaded or ( micro- 

 meter ' screw turned by a large milled- 

 head, at the upper end the cylinder 

 terminates in a brass table, which is 

 planed to a flat surface, or (which is 

 preferable) has a piece of plate-glass 



-cemented to it, to form its cutting bed. At one side is seen a small milled- 

 head, which acts upon a ' binding screw,' whose extremity projects into 

 the cavity of the cylinder, and serves to compress and steady anything 

 that it holds. For this is now generally substituted a pair of screws, work- 

 ing through the side of the cylinder, as in Fig. 120. A cylindrical stem of 

 wood, a piece of horn, whalebone, cartilage, etc., is to be fitted to the 

 interior of the cylinder so as to project a little above its top, and is to be 

 steadied by the 'binding screw;' it is then to be cut to a level by means 

 of a sharp knife or razor laid flat upon the table. The large milled-head 

 is next to be moved through such a portion of a turn as may very slightly 



1 It is difficult to convey by a drawing the idea of the real curvature of this 

 instrument, the blades of which, when it is held in front view, curve not to 

 either side but towards the observer; these scissors being, as the French instru- 

 ment-makers say, courbes sur leplat. 



