PREPARATION AND TREATMENT OF SPECIMENS. 275 



II. 



PREPARATION AND TREATMENT OF SPECIMENS. 



THERE are only very few bodies which can be spread out at once 

 upon the object-slide without further preparation, or be isolated by 

 mere pressure on the cover-glass ; the majority require a prelimi- 

 nary dissection into small portions, or must be examined in delicate 

 sections, the preparation of which requires special skill. The 

 proper treatment of objects, therefore, is always one of the principal 

 points in microscopic work. In order to render a given object as 

 accessible as possible for observation, and to become acquainted 

 with all the processes requisite for this purpose, it is of the first 

 importance to become expert in the manipulation of the preparing 

 instruments. Verbal discussion of this point must naturally be 

 confined to a short description of the means usually employed ; 

 matters supplemental must be reserved for practical instruction. 



The dissection of the object, as well as the separate preparation of 

 certain portions of it, is generally effected with a needle in more 

 difficult cases under a lens or a simple Microscope. 



An ordinary needle may be used for this purpose if it is firmly 

 fixed in a wooden handle. If better instruments are required, 

 needles of different shapes and sizes may be obtained, some, for 

 instance, with hook-shaped points, and others terminating in 

 small blades. Needles for difficult dissections must have fine 

 points, and when they become blunted should be sharpened ; but 

 those which are used merely for pressure upon the cover-glass or 

 for raising it when the objects are being moved, and also for 

 coarser dissections, should have blunt points, and should also be 

 somewhat stronger and rigid. The handle, especially for fine 

 needles, should permit their being changed at will and tightly 

 fixed by means of a metal collar. 



A skilful manipulation of the preparing needles is very import- 

 ant with many objects. The trouble caused by their preparation 

 is in many cases more than counterbalanced by the accuracy of 

 the observation thus attained*. Beginners usually fail by operating 

 with excessive quantities, and by not continuing the operation long 

 enough. 



