MEDIA FOR THE CULTIVATION OF BACTERIA. 59 



covered and protected from dust, is put into an ice-box, and 

 at the end of twenty-four hours the clot, consisting of fibrin 

 and of blood-corpuscles, is firm and sinks to the bottom of 

 the vessel, leaving a clear serum above and around it. This 

 clear serum may be siphoned or pipetted out and distributed 

 among sterilized test-tubes, which, after being plugged with 

 absorbent cotton-batting, are sterilized in Koch's serum steril- 

 izer by the low temperature process to be described later. 



Loeffler's modification of this method is generally used in all 

 municipal laboratories for the cultivation and diagnosis of 

 the bacillus of diphtheria : 



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 



