OF MICROSCOPIC OBJECTS. 125 



stroys them. He also advises the addition of two ounces of gela- 

 tine dissolved in eight ounces of water, to eight ounces of the 

 saturated solution of each salt ; but with this addition the hot- 

 water bath would be required to keep the injecting fluid liquid. 



27. Many of these are best mounted in balsam, in the same 

 manner as those made in the ordinary way ; whilst others are 

 best shown when preserved in liquids, for which purpose Goadby's 

 fluid may be employed. 



28. This mode of making injections with chromate of lead is 

 deemed by many the best, especially where one colour only is 

 employed. But it must be allowed that there is a little more 

 danger of failure where two separate fluids are used for the same 

 vessels. 



29. We will now consider the best manner of making trans- 

 parent injections, which, for many purposes, possess an undoubted 

 advantage over the opaque ones. But it must be remembered 

 that there are certain subjects to which no transparent injection 

 could be applied, as they are too thick when in their natural 

 state, and cutting would destroy all that beauty which is shown 

 by the different parts in their relative adaptation. For those 

 objects, however, which must be cut into sections to display their 

 wonders, or are naturally thin such as some of the finer tissues, 

 livers, kidneys, &c. transparency is a great acquisition, and ena- 

 bles us to understand the arrangement of the vessels more per- 

 fectly. Again, another advantage is the simplicity of the process ; 

 no hot water is needed with some preparations, either for the 

 subject or the injecting fluid, which runs into the minute vessels 

 thoroughly and easily, whilst the cost is small. 



30. For this kind of injection no colour is so commonly made 

 use of as Prussian blue. It is not a good one, as was before 

 stated, for any opaque object, as the light reflected from it appears 

 almost black ; yet by transmitted light no colour is more useful, 

 because its distinctness is equally great by artificial light and 

 ordinary daylight. The method of preparing this, as given by 

 Dr. Beale, is as follows : 



Glycerine 1 ounce. 



Wood naphtha, or pyroacetic acid 1^ drachm. 



Spirits of wine 1 ounce. 



