128 THE AMERICAN MONTHLY [Apr 



desired color, and dissolving- the same in alcohol but it is 

 advisable to use these varnishes for "finishing-'' purposes 

 only, as they are, after some time, extremely liable to chip, 

 and leave the glass. If, however, the best wax is used, the 

 risk of this happening is lessened. An excellent black 

 finishing varnish, free from brittleness, can also be made 

 by well mixing gold size with a small quantity of lampblack. 



Finishing Varnishes. — I have made excellent varnishes 

 by well mixing on glass, with a spatula, japan gold size with 

 the oil paints sold in compressible tubes for artists' use. 

 Only mix the quantity required for immediate use. Any 

 color can be got in this way. This will dry well, in say 12 

 hours, with a hard, level, washable gloss. In using the 

 sealing-wax varnish recommended, I have found that the 

 black is greatly improved by adding about twenty drops 

 of carbon-black solution, got by dissolving about two 

 drachms of carbon in a gill of methylated spirit, and that 

 the red is improved by adding about 1 dwt. (troy) of Ver- 

 million to it. The red settles if the vanish be not used 

 for about three hours, and therefore needs well shakingor 

 stirring before use. Gentle warmth, though not necessary 

 dries all the above varnishes much more quickly and 

 smoothly than its absence. — J. H. Henderson. 



Gelatin Culture Media. — The behavior of many sensi- 

 tive organisms, particularly parasites, depends entirely on 

 how the nutrient gelatin is compounded, and consequently 

 this should always be stated. The melting point of nutri- 

 ent gelatins increases as more gelatin is added. It de- 

 creases on addition of acids and alkalies and by long boiling. 

 Grape sugar or cane sugar added to nutrient gelatin fre- 

 quently restrains or entirely prevents liquefaction, while 

 at the same time it stimulates growth. For this reason 

 gelatin should be made with beef broth free from sugar. 

 Owing to the fact that commercial gelatin contains acid 

 salts, which are neutral or alkaline to litmus but retard 

 the growth of many organisms, the gelatin media should 

 first be rendered neutral to phenolphthalein, after which, 

 if desired, it may be acidified with particul.it acids. Acom- 



