460 BACTERIOLOGY. 



mistaking a sand granule for a colony. This objection 

 has been overcome by Sedgwick and Tucker, who employ 

 granulated sugar instead of the sand ; this, when brought 

 into the liquefied gelatin, dissolves, and no such error as 

 that possible in the Petri method can be made. 



SEDGWICK-TUCKER METHOD. On the whole, the 

 method proposed by Sedgwick and Tucker gives such 

 uniform results that it is to be recommended above the 

 others. It is as follows : 



The apparatus employed by them consists essentially 

 of three parts : 



(1) A glass tube of a special form to which the name 

 aerobioscope has been given. 



(2) A stout copper cylinder of about sixteen litres 

 capacity, provided with a vacuum-gauge. 



(3) An air-pump. 



FIG. 96. 



d cc Id 



The Sedgwick-Tucker aerobioscope. 



The aerobioscope (Fig. 96) is about 35 cm. in its 

 entire length; it is 15 cm. long and 4.5 cm. in diameter 

 at its expanded part ; one end of the expanded part is 

 narrowed down to a neck 2.5 cm. in diameter and 2.5 

 cm. long. To the other end is fused a glass tube 15 

 cm. long and 0.5 cm. inside diameter, in which is to be 

 placed the filtering material. 



Upon this narrow tube, 5 cm. from the lower end, a 

 mark is made with a file, and up to this mark a small 

 roll of brass- wire gauze (a) is inserted ; this serves as a 



