224 THE MICROSCOPE. 



Bichloride of mercury, one grain ; chloride of sodiuir», 

 ninety grains; distilled water, one pint: set aside, and, when 

 perfectly clear, decant and preserve in a stoppered bottle. 

 All preparations used in mounting, and objects themselves, 

 should be carefully preserved from dust. Ealsam should 

 be kept in a wide-mouthed bottle, over which a small 

 tumbler or cupping-glass must be inverted. It is ad- 

 visable to avoid the use of a cork, as it will be broken 

 in attempting to withdraw it, and portions will not only 

 adhere to the neck of the bottle, but are apt to get into 

 the balsam. Objects, and parts of objects, already prepared 

 and dry, may be kept neatly folded up in ivory-paper, as 

 it is not well to have too many objects in the turpentine 

 at the same time, in order to avoid confusion. Glass- 

 slides which are soiled with balsam can be cleaned with 

 turpentine and a piece of rag — the glass circles will require 

 to be soaked in turpentine to get rid of any balsam they 

 may happen to contract. When a greasy appearance is 

 present, it may be removed by a piece of rag moistened 

 with rectified spirit. Some remove it by rubbing the 

 glass with caustic alkali ; but as this liquid acts on flint- 

 glass, and sometimes makes it partially opaque or milky, 

 its use should be entirely discarded — a weak solution of 

 ammonia, or cyanide of potassium, answers the purpose best. 

 In order to demonstrate the internal structure of animal 

 tissues under very high magnifying powers. Dr. Beale^ says 

 the specimen must be placed in a 'viscid medium, and sub- 

 jected to considerable pressure to make it sufficiently thin. 

 Price's glycerine, having a specific gravity of 1,2 iO, and 

 a strong syrup, are the best adapted for preserving all soft 

 tissues. In practice, the specimen is first immersed in a 

 solution of weak glycerine or syrup, and the density ot 

 the fluid is gradually increased. In this way, and in the 

 course of* two or three days, the softest and most delicate 

 tissues swell out, and become more transparent ; but no 

 chemical change is produced in the specimens. The one 

 tiling to be observed is, that the strength of these fluids 

 should be increased very gradually until the whole of the 

 tissues are thorouglily penetrated and saturated by the 

 etrongest that can be obtained. Cerebral tissues, delicate 



(1) Bcale, " How to Work with the Microscope." 



