430 THE AMERICAN MONTHLY [Dec 



is not precipitated on boiling-. To this add 1.5 to two per 

 cent of ag-ar-agar, previously soaked in acidulated water, 

 and boil the mixture in a Koch's steamer until the ag-ar- 

 ag-ar is well dissolved. It must now be filtered throug-h a 

 hot water-funnel. The filtrate should be perfectly clear. 

 To the fittrate add four or five per cent of g"ly- 

 cerine. It may then be poured into test tubes and 

 sterilized. Besides the g-lycerine, 0.5 to two per cent of 

 g-rape sug-ar may be added ; this however g-enerally renders 

 the medium a little darker in color. 



Before adding- the caustic potash to the serous fluid, a 

 small quantity of it should be boiled in a test tube. If it 

 becomes practically solid, or contains large quantities of 

 albumin, the fluid must be diluted with at least twice its 

 bulk of distilled water ; and then to every 100 c. cm. of the 

 diluted fluid 2 c. cm. of KOH and 1.5 to two grams of agar- 

 agar are to be added. The serous exudation, after the 

 addition of the alkali, also forms a good liquid nutrient 

 medium for bacteria. 



Storaxas a Mounting Medium. — Permanent prepara- 

 tions can be mounted in storax, according to Dr. J. H. Pitf- 

 ard {Medical Record^ 1895, p, 547), if it be prepared as fol- 

 lows: — The storax is liquified on a water bath, then fil- 

 tered through two or three thicknesses of cheese cloth on 

 a hot-water funnel, and when cold mixed with an equal 

 weight of xylol. Shake well several timesthrough absorb- 

 ent cotton or Swedish filter-paper, and evaporate at a gen- 

 tle heat to the consistency of treacle. Finally, to each 

 two parts of the fluid add three parts of naphthaline mono- 

 bromide, and heat gently until a clear amber-colored fluid 

 is obtained. Preferably, the refractive index of the 

 medium should be brought to 1.625, by adding more of the 

 ingredient that may be found deficient, and the product 

 will then be found suitable for work with the highest 

 powers. 



Brown Cement, suitable for Microscopic ^A^ork. — The 

 Chemist and Druggist recommends either a thick solution 

 of shellac in vegetable naptha, or of gutta-percha in chloro- 

 form or bisulphide of carbon. 



