PREPARATION OF CLEARED SPECIMENS 713 



a few minutes mount in balsam. The times for which the specimen is 

 to be left in the various solutions depend upon its size and also upon the 

 amount to which it has been opened up to allow of free penetration 

 of the fluids. Prolonged application does no harm in ordinary work, 

 and the specimen may be left overnight in any stage if convenient. 



When studying the finer details of the chitinous parts it is best to 

 complete the dissection when the preparation has been cleared and taken 

 up to clove oil, as the object can then be dissected on the slide on which 

 it is to be mounted, thus obviating the risk of losing during the manipu- 

 lation any parts which are too small to be seen without the aid of a 

 microscope. It must be borne in mind, however, that prolonged immer- 

 sion in either alcohol or xylol, and to a lesser extent clove oil, makes 

 chitin brittle ; cleared preparations which require further dissection 

 before mounting should, therefore, be carried through as rapidly as 

 possible. 



Very thick chitinous parts may be rendered more easy to examine by 

 bleaching them after clearing. This is easily accomplished by the action 

 of chlorine gas, generated in a test tube from dilute 

 hydrochloric acid and chlorate of potash, or from ous parts' 

 chloride of lime. It is best to allow the gas to generate 

 for a few minutes, until the liquid is a rich yellow colour, and then to 

 put it aside till gas is no longer given off. A few minutes in this 

 solution will render the densest parts transparent. If the specimen is 

 placed in the mixture while effervescence is going on there is always 

 a risk of losing it, if it is small. 



Delicate Chitinous objects, such as the wings of small flies, or the thin 

 plates in the wall of the thorax, may be stained after a short period of 

 clearing. It is, of course, necessary to wash the speci- 

 men thoroughly to get rid of the alkali before applying preparations 8 

 the stain. Either a strong solution of watery eosin, 

 which stains the membrane between the chitinous parts more than the 

 chitin itself, or carbol fuschin, may be used. The length of time of 

 staining depends upon the density of the specimen, and it is convenient 

 to overstain in all cases, as either of these stains is easily washed out 

 by a trace of acid. 



When dealing with any minute object in an opaque solution great care 

 should be taken that the solution is filtered before use, and that there 

 are no particles of dust in the vessels used. A little care in this respect 

 will obviate the risk of mistaking a particle of dust or deposited stain 

 for the specimen. To find the specimen after staining, pour out the 

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