10 



Journal of Applied Microscopy. 



cylinder is provided with a flange 7 cm. 

 in diameter. The bearing surface of the 

 flange is 2 cm. wide and 1-2 cm. thick, 

 and is ground. 



Fig. 1. 



The upper and lower surfaces of the 

 flange must be parallel or nearly so, in 

 order to prevent the clamps from sliding 

 off. In the construction of the cylinder 

 it is essential that the ground surface be 

 at right angles to the inner wall of the 

 tube, and besides, that the inner diame- 

 ter of the tube be uniform throughout. 

 Should the tube be but very slightly nar- 

 rower near the flask, it would not permit 

 the introduction of the filter tube (Cham- 

 berland-Pasteur). In addition to this, 

 the cylinder must be made of thick, 

 strong glads, in order to withstand a 

 pressure of five or more atmospheres. 



Fig. 2. 



Figure 2 explains the device for obtain- 

 ing a perfectly tight connection between 

 the shoulder of the filter-tube and the 

 flange of the cyliTider. When putting the 

 parts together, it is best to place the 



cylinder with the flange end uppermost 

 on the ring of a retort stand. A rubber 

 ring (fig. ?, 1) is slipped over the steril- 

 ized filter-tube, and the latter is then 

 placed in the cylinder. When pressure is 

 afterward applied, this ring makes a per- 

 fect connection between the filter-tube 

 and the cylinder. If, however, the ring 

 is of soft rubber, the filter-tube is liable 

 to be broken on account of the high pres- 

 sure. Ordinary cloth-covered rubber, 

 from which the cloth has been torn, an- 

 swers the purpose very well. 



A similar rubber ring (flg. 2, 2) is 

 slipped over the neck of the filter-tube, 

 then the thick rubber ring (fig. 2, 3) is 

 placed in position, and, lastly, the brass- 

 plate (fig. 2, 4). Then the whole is 

 clamped tightly together by means of 

 three screw-clamps such as are used with 

 my Anaerobe Plate Apparatus. The 

 clamps must be tightened gradually and 

 equally In order to prevent the lower 

 closed end of the filter-tube from being 

 forced against the sides of the cylinder. 

 It is advisable to place on the closed end 

 of the filter-tube a very thin rubber band, 

 as shown in (fig. 1, e), which will serve 

 as an index of the lateral pressure. 



The thick rubber ring (fig. 2, 3) may be 

 replaced by small pieces of rubber of the 

 same thickness as the ring. The rubber 

 stopper, glass tube, and short rubber 

 tube (fig. 1, f.), having previously been 

 sterilized by steam, are now connected 

 with the filter-tube, and the entire ap- 

 paratus inverted and connected with the 

 sterile receiving-bottle (fig. 1, g). This 

 bottle is connected with a tube (fig. 1, h) 

 filled with sterilized cotton or sand, and 

 the latter with a small bottle (fig. 1, k) 

 for taking up any back flow from the 

 pump. A glass cock (fig. 1, 1) is pro- 

 vided to facilitate the admission of air. 



As is well known, there is a great dif- 

 ference in porcelain filters in regard to 

 rapidity of filtration; usually 250 cc. of 

 water can be filtered with the help of a 

 pump from three to five minutes. Bac- 

 terial fiuids of course filter much slower, 

 especially if they have not been first fil- 

 tered through paper. If the fiask con- 

 taining the fiuid to be filtered is connect- 

 ed with a cylinder containing air under 

 a pressure of four or five atmospheres, 

 this positive pressure can easily be added 

 to the negative pressure already present. 

 In this manner thick fluids, even blood 

 serum are easily and rapidly filtered. 



The small air cylinders with pumps, 

 such as are used by physicians for spray- 

 ing purposes, are very well adapted for 

 this purpose. Similar cylinders of com- 

 pressed air, as used for infiating bicycle 

 tires, answer the same purpose. Before 

 the pressure is applied, the stopper in 

 the neck of the flask is fastened down 

 securely by means of wires to the ring 



