CHOICE AND USE OF APPARATUS 



errors in compounding, and, in certain cases, will 

 save time; some of the stains, Haematoxylin for 

 example, are not fit for use till months after they 

 have been mixed with the other ingredients which 

 form the complete stain. 



Frequently when examining small but lively water 

 animals we may feel the necessity of some method 

 of sobering them. All the little organisms, both 

 plants and animals, which are provided with the 

 little whip-like structures mentioned so often in our 

 pages, are difficult to examine whilst they are in 

 motion. There are many substances, we might add, 

 which would kill them, but in doing so we shall nearly 

 always find that they contract to such an extent as 

 to lose all semblance of their natural shape, and be- 

 come useless as objects for our microscope. Should 

 our inclinations lead us in the direction of much study 

 of these little beings, we shall do well to keep handy 

 a small bottle of Rousselet's solution ; it is composed 

 of 2 per cent, solution of hydrochlorate of cocaine, 

 3 parts; Methylated Spirit, 1 part; water, 6 parts. 

 Any chemist will mix the solution for us. When we 

 have occasion to examine a too lively specimen, we 

 simply run a drop of the solution under the cover 

 slip, as described in our remarks on staining with 

 iodine, and the creature we are examining will 

 abandon its frolics and conveniently remain in a fully 

 expanded state. 



Many of our readers will be anxious to carry their 

 microscopic investigations to a more advanced stage 

 than we have reached in our pages. Some will have 



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