220 BACTERIOLOGY. 



a cloth instead of the usual lid, and when coagulated 

 firmly (90 C.) the tubes and their contents may, on 

 the following day, be sterilized in streaming steam at 

 100 C. without danger of the subsequent formation 

 of bubbles. Koch's serum coagulator (Fig. 22) is, 

 however, the most convenient apparatus. 



Serum may be preserved by placing it in flasks 

 which, after the addition of 5 per cent, of chloroform, 

 are sealed. When it is to be used it is filled into 



FIG. 22. 



Blood-serum coagulator. 



sterilized culture (test) tubes and sterilized by exactly 

 the same methods as are employed in sterilizing fresh 

 serum. The chloroform, being volatile, tends to dis- 

 appear at ordinary temperatures, but is quickly and 

 surely driven off at the temperatures used in steril- 

 izing. 



Serum may be efficiently sterilized, when great care 

 is used, by passing it through a Pasteur or Berkefeld 

 filter, under pressure. When so treated the fluid is 

 very clear and light-colored. 



Flasks, Dishes, Tubes, etc., Used for the Preservation of 

 Media and for other Bacteriological Purposes. The nutri- 



