56 STERILIZATION OF CULTURE MEDIA. 
which answers the purpose admirably, and which has the advantage 
of getting up steam very quickly and also of using comparatively 
little gas. 
The use of steam under pressure, by which higher temperatures 
are obtained, requires_a more expensive apparatus, made on the 
principle of Papin’s digester. The form manufactured by Miincke 
is one of the best. This is shown in Fig. 27. It is provided with a 
pressure gauge and a safety valve. A single sterilization in this ap- 
paratus, at a temperature of 115° C., for half an hour, will usually 
Mm 
Fie, 26, 
suffice, and for liquid culture media or for agar-agar this method is 
entirely satisfactory ; but a gelatin medium which is exposed to this 
temperature loses its property of forming a jelly at 20° to 22° C., and 
consequently its value as a solid culture medium. In practice the 
simpler form of apparatus in which streaming steam is used will be 
found to answer every requirement. To insure sterilization with 
this it is customary to resort to discontinuous heating, as heretofore 
described. The standard flesh-peptone-gelatin medium should, as 
a cule, be subjected to a temperature of 100° C. for ten minutes, at 
intervals of twenty-four hours, four days in succession. Bouillon, 
flesh infusions, and agar-agar jelly may be steamed for an hour at a 
time two or three days in succession. 
