METHODS FOR MICROSCOPIC STUDY OF BACTERIA 2l0 
are filled from a reservoir, usually a large funnel, the smaller end of 
which is provided with a short length of rubber tubing, into which a 
short glass tube, constricted somewhat at the outer end, is intro- 
duced. The flow is controlled by a pinch-cock, which constricts the 
rubber tubing midway between the funnel and the delivery tube. 
The cotton plug is removed from a test-tube and the delivery tube is 
introduced into the open end of it to a depth of about 2 inches. The 
pinch-cock is opened somewhat and the desired volume is allowed 
to flow in. The pinch-cock is then released to stop the flow, the 
Fig. 14.— Hot-air sterilizer. Lautenschlagcr form. (Park.) 
delivery tube removed, care being taken that no media touches that 
part of the test-tube where the cotton fits, so that it will not adhere 
to the sides of the tube, and the cotton plug is replaced. Usually 
about (S to 10 cc. of media are added to a tube. 
Sterilization of Media.— Media which contain neither coagulable 
proteins, gelatin nor carbohydrates are sterilized for fifteen minutes 
in an autoclave at a live steam pressure of 15 pounds (121.3° C). It is 
absolutely essential that all of the air in the sterilizer be displaced by 
