AZOLITMIN 2Q 



in the refrigerator. The next morning the milk beneath the cream should be 

 siphoned off. The short arm of the siphon should not reach the bottom of the flask 

 so as to avoid the sediment. Add sufficient litmus solution to this milk to give a 

 decided lilac tinge; tube and sterilize in the Arnold on three successive days. 



Litmus milk which apparently is as satisfactory as the above as regards nutritive 

 quality and cultural characteristics can be made from certain canned milks which 

 have not been condensed or sweetened and which do not contain chemical pre- 

 servatives. The "Natura" brand of milk is the one I have experimented with. 



Litmus Solution. A simple solution may be made by digesting the powdered 

 cubes repeatedly with hot water, mixing the extracts, and, after allowing them to 

 stand all night, decanting the solution from the inert sediment into a clean bottle. 



In litmus solution so made, however, a red dye is also present while calcium and 

 other salts are dissolved out. For bacteriological purposes a pure solution of the 

 blue dye should be used. This is called "azolitmin." It is freely soluble in water 

 but insoluble in alcohol. 



It can be conveniently prepared as follows: Weigh out 2 ounces of powdered 

 litmus; digest repeatedly with fresh quantities of hot water until all the coloring 

 matter is dissolved out; allow to settle, and decant off the fluid from the insoluble 

 powder. Add together the extracts, which should measure about a liter. Evapo- 

 rate down the solution to a moderate bulk, then add a slight excess of acetic acid, 

 so as to convert all carbonates present into acetates. Continue the evaporation, 

 the later stages over a water bath, until the solution becomes pasty. Add 200 c.c. 

 of alcohol, and mix thoroughly. The alcohol precipitates the blue coloring matter, 

 while a red coloring matter, together with the alkaline acetate present, remains in 

 solution. Transfer to a filter. Wash out the dish with alcohol and add this to 

 the filter. Wash the precipitate on the filter with alcohol. Dissolve the pure color- 

 ing matter remaining on the filter in warm distilled water and dilute to 500 c.c. 

 Azolitmin solution prepared in this way is more sensitive than ordinary litmus 

 solution. 



Azolitmin in powder can be purchased from dealers in chemicals. 



POTATO SLANTS 



Take Irish potatoes and scrub thoroughly with a stiff brush. Then pare off 

 generously all the outer portion. From the white interior cut out cylinders with a 

 cork borer. These cylinders should be of Y^ to % of an inch in diameter. Divide 

 a cylinder by a diagonal cut. This gives a plug with a flat base, the other extremity 

 being a slant. These potato plugs should be left in running water over night or 

 washed with frequent changes of water. This prevents the blackening of the plug. 

 Into a i-inch test-tube drop a pledget of absorbent cotton well moistened with water. 

 Then drop in the potato plug, base downward. Sterilize in the autoclave at 15 

 pounds for fifteen to twenty minutes, to insure sterility. 



For glycerine potato, soak the plugs in 6% glycerine solution for about one 

 hour. Then drop a pledget of absorbent cotton moistened with the same glycerine 

 solution into the test-tubes and follow it with the potato plug. Sterilize in the 

 autoclave. 



