The Microscope. 279 



have that clear-cut appearance nor are the colors so bright and firm 

 as those observed in balsam mounts. Then it has great avidity for 

 water and does not harden, which necessitates the sealing of the 

 cover-glass. This sealing if not done in the most perfect manner 

 will admit of the entrance of moisture with a consequent destruction 

 of the mount. Granting it well done, the wi'iter has doubts that 

 even pure glycerin acts as an indefinite preservative, though others 

 far more experienced in its use hold to the contrary. 



For temporary use, as in the inspection of sections to determine 

 their value for j^ermanent preservation in balsam it is excellent; for 

 the specimen can be taken directly from the water in which it has 

 been washed after staining, quickly examined, and if found accept- 

 able, can then be rewashed and put through the usual course. 



To obtain the best results pure glycerin should be employed, 

 though if its syrupy condition interfere, a little distilled- water with a 

 few di'ops of acetic acid can be added. The addition of these, 

 however, somewhat reduces its preservative quality. 



Farrant's Medium. — This preparation of glycerin is one of the 

 most eligible, for the reason that though it remains soft under the 

 cover-glass, the gum arabic which it contains causes it to harden at 

 the edges, thus facilitating the sealing process; or, when it is not 

 desired to I'etain the specimen for any great length of time, to dis- 

 pense with it altogether. It has the disadvantage, however, of not 

 being permanent, the gum which it contains tending to induce a 

 cloudy, granular condition after the lapse of a few years. 



The medium is prepared as follows: Take equal parts of dis- 

 tilled-water, glycerin and a saturated solution of arsenious acid — 

 saturated by boiling — mix well and add about one-half the bulk of 

 picked gum arabic, allow this to stand for two or three weeks, 

 stirring daily until the gum is entirely dissolved. Filter carefully 

 and decant into glass- stoppered bottles. If too much gum is added 

 the medium soon becomes cloudy; if too much glycerin it will not 

 harden as described above. 



Glycerine Jelly. — Kaiser's glycerin jelly, the formula of 

 which and methods for employing will be found on page 152 of this 

 journal, is an excellent medium and can be used in place of Farrant's 

 medium if desired. 



The mounting of all animal tissues, however prepared, can be 

 as well done with the media above described as if the list were larger 

 and more complex. The beginner should carefully experiment with 



