48 A MANUAL OF BACTERIOLOGY 



and the balls are in their turn forced out to the periphery of the 

 metal pot. The whole appliance is mounted on a cone, H, and 

 a centre, i, which are carried by two uprights attached to the 

 base plate, j ; one end of the shaft is attached to the electric 

 motor. 



The grinding action is brought about by retarding the revolu- 

 tion of the central cone, D. This has been effected by mounting 

 on the spindle of the central steel cone, D, a semi -cylindrical mass 

 of iron or lead, K, the weight of which must be such that when the 

 whole apparatus is rotated it is sufficient to hold the central cone 

 still. 



By retarding the cone in this way a drag is placed on the balls, 

 they slide to a certain extent over the inner surface of the pot and 

 exert a grinding action. 



Another form of mill which can be employed for the disintegra- 

 tion of bacterial cells, as in the preparation of tuberculin R, 

 consists of a porcelain pot containing porcelain balls. The pot, 

 which is closed with a screw-down lid, is mounted on a spindle 

 driven by an electric or other motor. By maintaining a speed 

 of 70-80 revolutions a minute for hours or days, the bacterial 

 cells are eventually disintegrated by the continual rolling and 

 collisions of the porcelain balls. 



See Hewlett's Serum Therapy, 1910 ; Hewlett, Proc. Eoy. Soc., 

 B, 1909 and 1911 ; Proc. Eoy. oc. Med., vol. iii, 1909-10 (Patho- 

 logical Section), p. 165 ; Barnard and Hewlett, Proc. Boy. Soc., 

 B., 1911. 



