Brook : Summary op Methods of Microscopical Research. 7 



STAINING MEDIA. 



The use of staining media in an aqueous solution has many dis- 

 advantages. In transferring an object from alcohol to such a solution 

 there is usually set up such a violent osmosis that whole groups of 

 cells may burst, and the whole object be spoiled. Again, a consider- 

 able maceration is liable to result from too long an immersion in 

 Beale's carmine. The staining media dissolved in alcohol, on the 

 other hand, are not open to these objections ; they penetrate the 

 object quicker, give a sharper and cleaner colour to the tissues, and 

 besides an object may be left in them for a considerable time without 

 fear of injury. Usually, therefore, an object preserved in alcohol 

 should be stained in an alcoholic solution, and passed through oil of 

 cloves to balsam for mounting, never from first to last being allowed 

 to touch water. Of course good results can often be obtained with 

 aqueous staining media, and in some cases they appear to be indis- 

 pensable, as, for instance, in the Turbellaria, which according to Dr. 

 Lang give a long way the best results when stained with picro- 

 carmine. 



Kleinenherg' 8 Soematoxylin. — This medium has been in use in the 

 Naples Aquarium for a long time, as it secures a good staining of the 

 nucleus, and requires but little trouble. Before staining, the object 

 must be got quite free from acid by washing frequently in alcohol, 

 and too much pains cannot be taken in this respect. The insufficient 

 freeing from acid does not often show itself at once, but after the 

 object is mounted in balsam, sooner or later it causes fading of the 

 colouring matter, which may go on until the object is entirely dis- 

 coloured. Dr. Mayer is of opinion that, with proper care in prepara- 

 tion, objects stained with Hoematoxylin get a little darker rather than 

 lighter after mounting. There is one great drawback to the use of 

 llamatoxylin, however, the solution loses its projDerties easily, becomes 

 discoloured, and throws down a precipitate. A fresh prepared 

 solution should be violet, with a decided leaning to blue, and must on 

 no account have a red tinge. If left to stand for a considerable time 

 it becomes slightly acid. In order to set it right again, the stopper 

 of an ammonia bottle should be held over the mouth of the bottle 

 containing the Hoematoxylin solution, so that an extremely small 

 quantity of ammonia gas mixes with the liquid. This, on shaking, 

 will restore the proper colour again. A very little more ammonia 

 would increase the precipitate, and make the liquid unfit for 

 use. 



