PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 1ST 



the dissection under Water, with which Alcohol should be mingled where 

 the substance 'has been long immersed in spirit. The size and depth of 

 the vessel should be proportioned to the dimensions of the object to be 

 dissected; since, for the ready access of the hands and dissecting-instru- 

 ments, it is convenient that the object should neither be far from its 

 walls, nor lie under any great depth of water. Where there is no occa- 

 sion that the bottom of the vessel should be transparent, no kind of Dis- 

 secting trough is more convenient than that which every one may readily 

 make for himself, of any dimension he may desire, by taking a piece of 

 sheet Gutta-percha of adequate size and stoutness, warming it sufficiently 

 to render it flexible, and then turning-up its four sides, drawing out one 

 corner into a sort of spout, which serves to pour away its contents when 

 it needs emptying. The dark color of this substance enables it to fur- 

 nish a back-ground, which assists the observer in distinguishing delicate 

 membranes, fibres, etc., especially when magnifying lenses are employed; 

 and it is hard enough (without being too hard) to allow of pins being 

 fixed into it, both for securing the object, and for keeping apart such 

 portions as it is useful to put on the stretch. When glass or earthenware 

 troughs are employed, a piece of sheet-cork loaded with lead must be pro- 

 vided, to answer the same purposes. In carrying-on dissections in such 

 a trough, it is frequently desirable to concentrate additional light upon 

 the part which is being operated-on, by means of the smaller Condensing- 

 lens (Fig. 86); and when a low magnifying power is wanted, it may be 

 supplied either by a single lens mounted after the manner of Ross's 

 Simple Microscope (Fig. 31, B), or by a pair of Spectacles mounted with 

 the 'semi-lenses,' ordinarily used for Stereoscopes. 1 Portions of the body 

 under dissection being floated-off when detached, may be conveniently 

 taken up from the trough by placing a slip of glass beneath them (which 

 is often the only mode in which delicate membranes can be satisfactorily 

 spread out); and may be then placed under the Microscope for minute 

 examination, being first covered with thin glass, beneath the edges of 

 which is to be introduced a little of the liquid wherein the dissection is 

 being carried-on. Where the body under dissection is so transparent, 

 that more advantage is gained by transmitting light through it than by 

 looking at it as an opaque object, the trough should have a glass bot- 

 tom, and for this purpose, unless the body be of unusual size, some of 

 the Glass Cells already described (Figs. 121-123) will usually answer very 

 well. The finest dissections may often be best made upon ordinary slips 

 of glass; care being taken to keep the object sufficiently surrounded by 

 fluid. For work of this kind no simple instrument is more generally 

 serviceable than the Laboratory Dissecting Microscope (Fig. 35), which 

 will carry any power from 3-inch to a l-4th inch; whilst the Stephenson 

 Erecting Binocular (Fig. 47) may be used with the like supports for the 

 hands, when a higher power is preferred. 



181. The Instruments used in Microscopic dissection are for the most 

 part of the same kind as those which are needed in ordinary minute An- 

 atomical research, such as scalpels, scissors, forceps, etc.; the fine instru- 



1 The author can strongly recommend these Spectacles, as useful in a great 

 variety of manipulations which are best performed under a low magnifying 

 power, with the conjoint use of both eyes. Where a higher power is needed, re- 

 course may be advantageously had to Messrs. Beck's 3-inch Achromatic Binocu- 

 lar Magnifier, which is constructed on the same principle, allowing the object to 

 be brought very near the eyes, without requiring any uncomfortable convergence 

 vof their axes. 



