42 CULTIVATION OF BACTERIA. 



serum will contain air bubbles. Blood-serum can be pre- 

 served in bottles or flasks by adding an excess of chloro- 

 form. The chloroform is evaporated subsequently, when the 

 medium is again sterilized. 



Loeffler's blood-serum : This is a mixture of blood-serum 

 and bouillon. 1 part of a 1 per cent, glucose-bouillon is 

 added to 3 parts of liquid blood-serum. After the mixture 

 is transferred to test-tubes it is sterilized and solidified as 



FIG. 10. 



Chamber for sterilizing and solidifying blood-serum. (Koch.) 



described above. This medium is used especially for mak- 

 ing cultures of the diphtheria bacillus. 



Alkaline blood-serum : This also is used for the diphtheria 

 bacillus. It consists of 100 c.c. of blood-serum and from 1 

 to 1.5 c.c. of a 10 per cent, solution of sodium hydrate. 



Milk: After perfectly fresh milk has been skimmed, it is 

 placed in test-tubes and sterilized. To determine acid-pro- 

 duction, sufficient blue litmus is added to color the milk. 

 The litmus solution should always be freshly prepared, as it 

 spoils very rapidly. 



Dunham's solution: This is used to detect the aromatics 



