160 PATHOGENIC ORGANISMS 



ease, or water, it is almost invariably intermittent or transitory 

 with the consequence that by the time an outbreak has oc- 

 curred and can be traced to the milk supply it is almost hopeless 

 to expect to isolate the infecting organism. This, however, 

 should not deter those responsible for the investigation of such 

 cases from attempting the isolation of B. typhosus. 



Isolation of B. Typhosus. Jackson and Melia 18 recommend 

 inoculating the sample into lactose bile and incubating at 37 C. 

 The cultures are to be transplanted in varying dilutions into 

 Hesse agar and examined after twenty-four hours at 37 C. 

 On this medium B. coli forms small succinct colonies; B. 

 typhosus is most characteristic on plates containing but few 

 colonies; colonies of a large size are then formed, often several 

 centimetres in diameter, and consisting of a broad translucent 

 or scarcely turbid zone between a white opaque centre or nucleus 

 and the perfectly circular narrow white edge. Tonney et al. 19 

 found that lactose bile is inhibitory to B. typhosus as well as to 

 the colon group of organisms and this is confirmed by the au- 

 thor's experience. 



The following method, which is an adaptation of Browning 

 and Thornton's method 40 for the isolation of typhoid bacilli 

 from faeces, can be recommended for the isolation of B. typhosus 

 from milk. Centrifugalise 50 c.cms. of the sample for twenty 

 minutes at 2000 to 2500 revolutions per minute. Remove the 

 cream layer to a sterile tube and place it in a water bath at 

 37 to 40 C. Draw off the skim milk by means of a fine glass 

 tube attached to a suction pump until about 3 c.cms. remain. 

 After thoroughly distributing the sediment throughout the 

 liquid it is inoculated into three brilliant green peptone^tubes, 

 one cubic centimetre being placed in each tube. The molten 

 cream layer should be similarly treated as a proportion of the 

 organisms may be trapped by the rising fat globules during the 

 centrifugalising process. The brilliant green medium is pre- 

 pared by steaming a 2 per cent peptone solution, containing 

 0.5 per cent of sodium chloride, for forty-five minutes and 

 filtering after making the reaction slightly alkaline to litmus. 



