THE MEDIA OF THE CULTIVATION OF BACTERIA. 57 



Beef or mutton-blood is collected in the usual way, and to 

 8 parts of the clear serum 1 part of glucose-bouillon is added. 

 This mixture distributed among test-tubes is sterilized and 

 hardened in a slanting position in a steam sterilizer at a tem- 

 perature between 80 and 90 C., for an hour each day dur- 

 ing a whole week. 



3. The serum of ascitic fluid and (4) the fluid of hydrocele 

 are sometimes used for the cultivation of bacteria, and are 

 prepared in the same manner as ordinary blood-serum. 



5. Urine. 



Urine may also be used for the cultivation of bacteria. 

 For this purpose it is obtained by means of a sterilized cathe- 

 ter directly from the bladder, where it is generally sterile. 

 It is safest, however, to sterilize it by steam for one hour 

 before use. 



6. Pasteur's Solution. 



Filtered water, 100 parts ; 



Cane-sugar, 10 " ; 



Ammonium tartrate, 1 part. 



With the addition of 1 part of the ashes of yeast this was 

 formerly extensively used as a culture-medium, but is now 

 seldom used. 



7. Bouillon. 



Bouillon is the most frequently used of all the fluid media. 

 It is prepared as follows : 1 pound of fresh lean beef is 

 chopped up very fine and covered with 1 liter of sterilized 

 water, and put into an ice-box for twenty-four hours, after 

 which the aqueous extract is obtained by filtration through 

 muslin by pressure, sufficient water being added if necessary 

 to make up the original liter. To this filtrate 10 grams of 

 peptone and 5 grams of sodium chloride are added, and the 

 whole is cooked on a water-bath or in an enamelled iron 

 kettle for a half-hour, after which sufficient of a saturated 

 solution of sodium carbonate is added drop by drop to give 

 the mixture a slight alkaline reaction. This, after cooking 



