OF THE MICROSCOPE. 201 



DAMAB MEDIUM. Gum damar has been recently introduced 

 amongst the materials used by microscopists, and with some ii> 

 has found great favor. Carpenter speaks highly of it. Dia- 

 toms are said to show better in it than in balsam, and for 

 delicate physiological preparations, especially transparent in- 

 jections, it is very excellent. It is thus prepared: Half an 

 ounce of gum damar is dissolved in one ounce of oil of turpen- 

 tine, and half an ounce of gum mastic in two ounces of chloro- 

 form. The solutions are filtered and mixed. 



Ordinary damar varnish, such as is used by painters, is some- 

 limes sold for microscopical purposes, but it does not give 

 satisfactory results. 



Preparations which have been preserved and mounted in 

 balsam or damar are very durable, while those that are 

 mounted in fluids are a source of continual annoyance and loss. 



Many microscopists, therefore, exclude from their cabinets 

 all preparations mounted in liquid on the ground that sooner 

 or later they will become worthless. And many of our best 

 dealers refuse to have anything to do with them. Neverthe- 

 less, as Frey well says, " the natural condition of the tissues is 

 completely represented only when mounted in a moist condi- 

 tion. This method permits of the most accurate recognition of 

 delicate textural relations, pale cells and fibres, etc., and should 

 not be omitted with any tissue in the production of histologi- 

 cal collections." 



GLYCERINE. At the head of the list of preservative media 

 for moist preparations stands glycerine. "Its strong refrac- 

 tive power, its property of combining with water, and of at- 

 tracting the same from the atmosphere, render it an invalua- 

 ble medium for mounting animal tissues containing water. 

 It may be truly said, that what Canada balsam is to dry tissues, 

 glycerine is to moist ones." (Frey.) Much of the glycerine in 

 market is very impure, and although the impurities do not 

 show themselves very strongly at first, they soon become mani- 

 fest by the darkening of the liquid, (owing probably to the 

 presence of lead), ?.nd the formation of a cloudy precipitate. 

 Dr. Beale strongly recommends Price's glycerine, and we have 

 found it very excellent. 



