filter-pai 



FILTRATION OF BACTERIA. 



Iter-paper. Different porous materials have been used for bacterial niters; 

 of which especially suitable are porcelain, infusorial earth and asbestos. The 

 nitration apparatus consists of the respective filter and the receptacle which 

 receives the filtrate. Filtration takes place by differences in pressure, where 

 either the fluid is forced through by high pressure or sucked through by a 

 vacuum formed in the receiving vessel. The following are some of the 

 filters most commonly in use. 



1. CHAMBERLAIN'S CYLINDER FILTER, F, used in the Pasteur Institute at Paris. The 

 filter cylinder is made of infusorial earth and may be attached to any faucet. 



2. PUKAL FILTER, made of burnt kaolin, is used especially for the nitration of large 

 quantities of fluid. The filter b is placed into the beaker e containing the toxin and 

 bacterial fluid. The former is then closed by a rubber stopper, perforated by a central 

 opening through which runs a glass tube bent at right angles, and this in turn is connected 

 with either an air or water pump for producing a vacuum inside of the filter. Between 

 the filter and vacuum pump can be interposed a sterile jar a. (Figs. 9 and 10). 



FIG. ii. Relchel filter. 



FIG. 12. Lilliputian filter. 



3. THE REICHEL FILTER (Fig. n) consists of a glass receiver A, having a side neck c 

 and at the bottom a tube-like outlet d. A porcelain filter B fits into the glass jar and 

 rests upon the margin of the flask by means of a broad collar. The point of junction is 

 made air tight by means of a rubber cap with a central opening, through which the 

 cylinder can be filled. When in use d is shut off by a rubber tube with a pinch cock and 

 c in which lodges a small piece of cotton is connected with a water pump that is instru- 

 mental in bringing about a vacuum. The function of d is to allow the removal of samples 

 of the filtrate and finally to obtain the entire filtrate. 



4. THE LILLIPUTIAN FILTER, candle-like in shape, and made of infusorial earth, is 

 employed for the filtration of very small quantities. The filter is cemented upon a metal 

 tube which is screwed, so that it is air tight, into a well-fitting glass cylinder open at the 

 top. The tube is passed through a rubber cork which tightly closes an exhaust flask. 



