50 



THE ART OF MAKING MICROSCOPE SLIDES 



Crustaceans 



lected, they should all be narcotized before 

 killing, and should be killed in 95% alco- 

 hol and stored in this fluid, with a trace 

 of glycerol, until required. When it is de- 

 cided to mount them they are removed 

 from 90% alcohol to 70% alcohol. After 

 they have been permeated with this, 

 glycerol is added little by little until the 

 total concentration of glycerol is such 

 that, if the alcohol be evaporated, a 50% 

 glycerol-water mixture will be left. The 

 final evaporation is best done at a tem- 

 perature of 30° to 40°C. and is very con- 

 veniently conducted in a desiccator 

 through which a current of air is drawn 

 with any aspirator device. If the specimens 

 are not very minute, it is desirable that 

 the 50 % glycerol should be poured off and 

 replaced with the molten mounting me- 

 dium in which the specimens should re- 

 main for an hour or two before mounting. 

 Do not, however, transfer to the molten 

 jelly more specimens than you are able to 

 mount at one time, since prolonged soak- 

 ing in the molten medium tends to soften 

 them. The required number of slides are 

 then warmed and a specimen, in a large 

 drop of molten medium, placed on each. 

 The specimen is then arranged with a 

 needle and chilled rapidly. If there is not a 



large domed drop of medium over the top 

 of the specimen, further medium is added 

 from a pipet until there is a thick layer. 

 When all the specimens have thus been 

 mounted in the required position with a 

 big dome of cooled jelly above them, a 

 covershp thinly smeared with 50% glyc- 

 erol is laid on each. All of the shdes may 

 be provided with coverslips resting loosely 

 on them before going further. The alumi- 

 num rod shown in Fig. 22 is now warmed 

 and pressed down on the coverslip until 

 the latter has come to rest on the speci- 

 men, or on the walls of the cell. A httle 

 practice is required to be able to do this 

 without pressing down either so hard that 

 one crushes the specimen or so long that 

 one melts the jelly surrounding it. 



If these specimens are mounted in a 

 medium which does not contain sufficient 

 glycerol, and which accordingly cracks 

 and dries out when they are transferred to 

 a drier environment, they may be re- 

 mounted without very much difficulty by 

 cracking the covershp, soaking the speci- 

 men in 50% glycerol for a week or two, 

 then removing the rest of the coversUp and 

 remounting as though one had a fresh 

 specimen. 



