38 



LABORATORY EXERCISES IN BACTERIOLOGY. 



the liquids, particularly solutions of organic matter, pass but slowly through the rather 

 compact porcelain, it is commonly necessary to attach to the receiving flask some form 

 of vacuum pump, an ordinary water pump connected with a neighboring faucet being 

 usually used. Care should be exercised to have the connection between the pump and 

 the receiver of heavy, non-collapsible tubing and so arranged that there is no danger of 

 reversal of the flow of water so as to enter the receiver. Before setting up such filtration 

 apparatus it is essential that the various parts be sterilized. Those parts made of glass, 

 as the heavy receiving flask and funnel, having been well washed, are to be plugged with 

 cotton and baked in the ordinary manner or sterilized in the autoclave. The rubber 

 connection and the perforated rubber stopper should be soaked in a solution of some 

 suitable disinfectant (as 1 : 1000 solution of mercuric chloride, or a three or four per cent. 



FIG. 9. KITASATO FILTER. 



FIG. 10. FILTER REVERSED IN A PERCO- 

 LATOR FILLED WITH WATER IN ORDER 

 TO WASH BACK SOLID PARTICLES LODGED 

 IN ITS WALL. 



solution of carbolic acid) and well rinsed in sterile water. The porcelain bougie should 

 have been wrapped in paper, the open end of the bougie being marked on the outside, 

 and carefully sterilized in the autoclave. All of the parts having received such atten- 

 tion, the funnel is adjusted in the perforated rubber stopper, the connecting rubber tube 

 fitted to the lower end of the funnel ; and the open end of the bougie being exposed from 

 its paper cover is adjusted in the lower end of the rubber connecting tube, which is bound 

 to the latter and to the lower end of the funnel by several ties of sterile copper wire. 

 The bougie is then freed from its wrapping paper and placed in the receiving flask and 

 the rubber stopper tightly fixed in place. The pump connection is then made with the 

 side tube of the receiving flask, the fluid to be sterilized introduced into the funnel, and 

 the pump cautiously started. At best filtration is a slow process, and if proceeding at 

 all satisfactorily should not be interfered with, since the least extra force of current 



