44 PHARMACEUTICAL BACTERIOLOGY. 



tionally on three successive days (one hour each day) at a temperature of 

 80 C. These tube slants are now ready for the physician. 



To prevent evaporation of the medium in the test-tubes, cover the cotton 

 plug and upper end of tube with tin foil fastened with thread, and dip into 

 melted paraffin several times. Tubes thus sealed can be kept for a year or 

 more without any considerable shrinking of the medium. Dip the tin foil in 

 a 1:2000 corrosive sublimate solution before capping on tubes. 



A simpler way is to use rubber caps which are especially made to fit over 

 the end of the test-tube and the cotton plug. These rubber caps must be 

 sterilized before applying them, for which purpose the 1-2000 corrosive 

 sublimate solution will be found satisfactory. Rubber stoppers may also be 

 used but they are more expensive and inferior to the rubber cap or the tin 

 foil with coat of paraffin. 



C. Liquid Blood Serum. Obtained as for Loeffler's serum. Sterilize 

 fractionally at a temperature of from 56 to 58 C. for one hour on each of 

 six days. The serum will be liquid and clear. 



D. Milk. Secure fresh milk directly from cow, or, if in cities, demand 

 certified milk. Keep on ice, in a covered jar, for twenty-four hours. Siphon 

 off the middle portion, rejecting cream and sediment. Sterilize like Loeffler's 

 blood serum. Litmus milk is prepared by adding i per cent, of azolitmin 

 before sterilizing. This indicator will show whether or not acids are formed 

 by the microbes which may be cultivated in the milk. Only pure milk will 

 answer the purpose. Milk to which preservatives (formaldehyd, salicylic 

 acid, borax, boric acid) have been added must not be used. 



E. Peptone Solution. The medium is employed to test for the develop- 

 ment of indol by certain bacteria. It consists of 



Peptone, 10 gm. 



Salt, 5 gm. 



Distilled Water, 1000 c.c. 



Boil, filter, and sterilize as for bouillon. The bacteriological indoF test 

 is of great importance in medical practice, and the chances are that physi- 

 cians will require this medium. However, sugar-free beef broth is also used 

 for this test; in fact, it is generally preferred. Beef contains a small amount 

 of muscle sugar, which must first be removed. 



F. Sugar-free Bouillon. Grind the fat-free beef through a meat grinder; 

 add water, and inoculate at once with a pure culture of Bacillus coli communis, 

 and allow to incubate for twelve to fifteen hours at 38 C., then boil, filter, 

 add peptone and salt, and prepare like bouillon; or, inoculate nutrient 

 bouillon with the colon bacillus and prepare as above. However, before 

 using the medium it should be tested for indol, as it has been proved that 

 B. coli communis may form indol in beef extract. The indol test in bacterial 

 cultures is made by adding two drops of concentrated sulphuric acid and one 



