456 PEEPAEATION, MOUNTING, AND COLLECTION OF OBJECTS 



ground, which assists the observer in distinguishing delicate mem- 

 branes, 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 earthen- 

 ware troughs are employed, a piece of sheet-cork loaded with lead 

 must be provided 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; 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, 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 bottom : 

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

 glass cells already described (figs. 376-377) 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 sur- 

 rounded by fluid. For work of this kind no instrument is mon- 

 generally serviceable than the erecting binocular form of stand as 

 recently modified for dissecting purposes by Swift. It is an instru- 

 ment which combines conveniences and supplies wants which only 

 a worker at dissection could have known. It is illustrated in fig. 

 387, and will be thoroughly suitable for all the work in which it will 

 lie required, from diatom mounting to the most delicate dissections. 

 The supports for the hands on either side of the stage have an ex- 

 tremely suitable curve, and the instrument lends itself admirably to 

 the work. 



The instruments used in microscopic dissection are for the most 

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

 anatomical research, such as scalpels, scissors, forceps, etc.; the fine 

 instruments used in operations upon the eye. however, will commonly 

 lie found most suitable. A pair of delicate scissors, curved to one 

 side, is extremely convenient for cutting open tubular parts ; 

 these should have their points blunted, but other scissors should 

 have fine points. A pair of very fine-pointed scissors (fig. 388). 

 one leg of which is fixed in a light handle, and the other kept 



The e m.i\ lie reeoiumeiided as useful in a great variety of manipulations which 

 best performed under ;i low magnifying [tower, with the conjoint use of both eyes. 



When- H lii'jli | mwer is i led. recourse may lie advantageously had to Messrs. 



I'.eeK .; ini I :irlu uinatic binocular magnifier, which is constructed on the same 



iple, allowing t he object to lie brought. \ ery iie;ir (lie e\e>, without requiring any 



iiiicoiiit'ui 1;ib!e convergence cif their :i\es. 



