184 Culture Media and Bacteria Cultivation 



too rapidly it is certain to bubble, so that the desirable 

 smooth surface upon which the culture is to be made is 

 ruined. 



Like other culture media, blood-serum and its combina- 

 tions may be sterilized in the autoclave and much time 

 thus saved. The serum should, however, first be coagu- 

 lated, else bubbling is apt to occur and ruin its surface. 

 The autoclave temperature unfortunately makes the prep- 

 aration very firm and hard, considerable fluid being pressed 

 out of it. 



It is said that considerable advantage is secured from the 

 addition of neutrose to blood-serum, which prevents its coag- 



Fig, 34. Koch's apparatus for coagulating and sterilizing blood- 



serum. 



ulating when heated. It can then be sterilized like bouillon 

 and can subsequently be solidified, when desired, by the 

 addition of some agar-agar. 



Fresh blood-serum can be kept on hand in the laboratory, 

 in sterile bottles, by adding an excess of chloroform. In the 

 process of coagulation and sterilization the chloroform is 

 evaporated ; the serum is unchanged by its presence. 



Lbffler's Blood=serum Mixture, which seems rather 

 better for the cultivation of some species than the blood- 

 serum itself, consists of i part of a beef-infusion bouillon con- 

 taining i per cent, of glucose and 3 parts of liquid blood- 

 serum. After being well mixed the fluid is distributed in 



