60 



STERILIZATION OF CULTURE MEDIA. 



In Fig. 30 the Pasteur-Chamberland filter is shown as arranged 

 for the filtration of -water. A is the hollow porcelain cylinder, which 

 is enclosed in a metal case, D. The metal case is tightly clamped 

 against a projecting shoulder at the lower part of the porcelain filter, 

 a ring of rubber being interposed to secure a tight joint. When 

 water under pressure is admitted to the space E, between the cylin- 

 der of porcelain and the metal case, it slowly filters through, and, 

 running down the inner wall of the filter, escapes at B into a recep- 

 tacle placed to receive it. If we fill the space E with a liquid cul- 

 ture of bacteria and apply sufficient pressure (one or two atmo- 

 spheres), a clear filtrate is obtained which is entirely sterile if the 

 porcelain filter is sound and made of proper material. After the 



FIG. 31. 



filter has been in use for some time, however, it may permit the pas- 

 sage "of bacteria, and it will be necessary to subject it to a high tem- 

 perature for the purpose of destroying all organic matter contained 

 in the porous porcelain. 



We may use the Chamberland filter without a metal case by im- 

 mersing it in a cylindrical glass vessel containing the liquid to be fil- 

 tered, as shown in Fig. 31. The porcelain cylinder is connected with 

 an aspirator bottle, , and a small Eiienmeyer flask, b, is interposed 

 to catch the filtrate when it overflows from the interior of the filter. 

 Of course all the necessary precautions must be taken with reference 

 to the sterilization of the interior of the bougie, of the flask b, and of 

 the rubber tube connecting the two. 



Another arrangement of the Pasteur-Chamberland filter for labora- 

 tory purposes is shown in Fig. 32. In this form of apparatus a 



