42 PURE CULTURES OF 



a placed at an angle to each other. I have added these 

 windows as some attach importance to them. In the figure 

 they are shown as rectangular, but recent experiments show 

 that they are best circular. According to my own experience, 

 however, they are advantageously omitted. Through the 

 top passes a stirrer b, the lower end of which is fitted with 



FIG 



two blades, one carrying a sheet of rubber cut in such a way 

 that when rotated it comes into contact with both the bottom 

 and the sides of the cylinder. From the top there passes a 

 doubly bent tube c and by opening its cock, connection is 

 made with the inside of the cylinder. The lower free end 

 of the tube dips under water in the vessel d. This tube 



