CLEARING AGENTS AND MOUNTING MEDIA 5OI 



must be removed before a satisfactory examination can be made. For 

 driving out air 70 per cent, or stronger alcohol should be used, but this is 

 not a desirable medium for general use, as it evaporates rapidly and allows 

 the specimens to dry up. However, this medium is excellent for bringing 

 out details of structure, and may be profitably employed when a hasty 

 examination is to be made. It can be replaced by water or other media 

 as desired. 



Equal parts of water and glycerine furnish one of the best and most 

 useful mounting media. This mixture is especially desirable when delicate 

 markings are not brought out in water. It acts as a clearing agent, and 

 although the action is somewhat slow, it will render most specimens clear 

 enough for examination. Equal parts of water, glycerine, and alcohol 

 make a reagent to be preferred to the above in many respects, and is the 

 most useful of the simple and cheap reagents. This mixture penetrates 

 tissues well, acts as a clearing agent, and does not dry up. Specimens 

 may be kept in it for days or even weeks. 



In the examination of many specimens it is necessary to use a strong 

 clearing agent, and it is frequently desirable to have one that acts rapidly. 

 Chloral hydrate, made by dissolving five parts of chloral hydrate crystals 

 in two parts of .water, is one of the most common and useful clearing agents. 

 Its action is rapid, but it is not a good medium for mounting in many 

 cases, since delicate markings are not clearly brought out by it. In many 

 specimens starch is dissolved by this reagent, and it should never be used 

 when accurate measurements of starch grains are to be made. However, 

 chloral-hydrate solution with iodine added is the best and most reliable 

 agent for the detection of starch, and is especially recommended where 

 starch occurs in small quantities or is likely to be obscured, as in chloro- 

 plasts or by proteid substances. 



A clearing agent to be preferred to the above for general purposes may 

 be made by mixing i part of 95 per cent, alcohol, i part glycerine, i part 

 water, and 4 parts saturated aqueous solution of chloral hydrate. This 

 mixture gives a reagent fairly rapid in action, and also serves well as a 

 mounting medium. It is the most useful clearing agent and can be em- 

 ployed in more cases than any other. 



Potassium hydrate in 2 to 10 per cent, aqueous solution is valuable 

 as a clearing agent, and also serves well as a macerating agent. It is'rapid 

 in action, and dissolves starch. Acetic acid, 20 per cent., and hydrochloric 

 acid, 10 to 20 per cent., may be found exceedingly useful as clearing agents 

 in many cases. They are often valuable in removing starch from speci- 

 mens where it may interfere in an examination. 



In the preparation of specimens which are exceedingly difficult to clear, 

 or in handling coarse powders where the fragments are so large that they 

 must be broken up by macerating before mounting, javelle water and 

 Schultz's macerating fluid will be found useful. 



