46 A MANUAL OF BACTERIOLOGY 



The pot with its contents is immersed in a vessel of liquid air or 

 other freezing mixture and the bacterial mass is ground. 



After grinding, the ground material is made up with distilled 

 water or with 0-1 per cent, sodium hydrate so as to form a 10 per 

 cent, solution (calculated on the original weight of the moist 

 bacterial paste) ; this is centrifuged, and the fluid is filtered 

 through a sterile Berkefeld filter. 



The filtrate thus obtained is the endotoxin, and is used to 

 immunise horses and other animals in the same manner as with 

 any other toxin ; it should be used as fresh as possible. The- 

 amounts of a typhoid or cholera endotoxin employed for immunis- 

 ing must at first be small, 0-2-0-5 c.c., as it produces considerable 

 disturbance on injection, and the amount is gradually increased. 

 After some weeks' treatment a dose of 2030 c.c. may be injected. 

 When tests show that the serum has attained the necessary 

 potency, the horse is bled and the serum obtained and bottled. 



The endotoxins also possess immunising properties to a high 

 degree, and may be used as prophylactic or as curative vaccines ; 

 they markedly raise the opsonic index. 



Another machine has been devised by Barnard for disintegrating 

 bacterial and other cells. It is supplied by Messrs. Baker, of High 

 Hoi born, and is depicted in Fig. 1. 



The containing vessel consists of a phosphor-bronze body, A, in 

 which five hardened steel balls, B, are placed. The shape of the 

 containing vessel is such that when these balls are at its periphery 

 they accurately fit the inner side of the vessel. The balls are 

 evenly distributed round the vessel by means of a cage, c, and 

 during the time they are running this cage ensures that they are 

 equidistant and do not collide one with another. At the centre 

 of the metal vessel is a steel cone, D, which is of such a size that 

 it keeps the balls in their proper position in close contact with the 

 periphery of the containing vessel. The vessel is closed by a 

 screw cap, E, through which the steel cone passes, and in which it 

 is free to rotate. Over the whole of this a metal cylinder, F, is 

 placed, and is screwed down, completely sealing the upper open- 

 ing in the metal vessel. In the top of this metal cylinder a steel 

 bearing, G, is placed, which has freedom of movement in a hori- 

 zontal direction, but is kept down on the top of the steel cone by 

 the action of a spring. It therefore follows that when this metal 

 cylinder is screwed down the steel cone is pressed on to the balls, 



