220 BACTERIOLOGY. 
acloth 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- 
