14 THE STRUCTURE OF 



object under the Microscope. If this is the case, 

 only a low power should be used, and the object 

 may be placed on a glass slide, without any glass 

 over, and two needles with small wooden handles 

 employed ordinary sewing needles, with their eyes 

 stuck in the handle of a hair-pencil, will answer 

 very well. Even when dissection is not to be 

 carried on under the Microscope, a pair of needles 

 of this sort, for tearing minute structures in pieces, 

 will be found very useful. 



When opaque objects are to be examined, the 

 light from the mirror may be shut off, and the aid 

 of the bull's-eye condenser called in. The object 

 being secured in the forceps attached to the stage 

 or laid upon a slide, the light is allowed to fall on 

 it through the condenser. The object-glass must 

 be focussed in the same manner as for transparent 

 objects, till the best distance is secured for examin- 

 ing it. The petals of plants, the wings and other 

 parts of insects, with many other objects, can only 

 be examined in this way. 



Even the beginner will find it useful to keep by 

 him some little bottles, containing certain chemical 

 re-agents. Thus, a solution of iodine is useful to 

 apply to the tissues of plants, for the purpose of 

 ascertaining the presence of starch. This solution 

 may be made by adding five grains of iodine and 

 five grains of iodide of potassium to an ounce of 

 distilled water. Strong sulphuric acid will be 

 found useful in rendering soft the tissues of both 

 plants and animals ; and in conjunction with iodine 

 it is a test for the presence of cellulose. The 

 strong solution of potash (liquor potassse) can also be 

 employed with advantage in softening and making 

 clear opaque animal and vegetable substances. 

 Nitric acid has even a greater solvent power than 

 sulphuric acid, and may be used for the same 



