236 Cultivation of Micro-organisms 



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. 46. 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. 



Loffler'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 



