164 PATHOGENIC ORGANISMS 



Examination. Morgan's No. 1 Bacillus is very suscep- 

 tible to the action of brilliant green and will not appear on the 

 rebipelagar plates in the enrichment method for isolating the 

 organisms of the Gaertner group. The best procedure is to 

 inoculate the centrifugalised deposit from about 40-50 c.cms. 

 of milk into a number of tubes of neutral red lactose bile salt 

 agar and incubate for twenty-four to forty-eight hours after 

 mixing and pouring into petri plates. All colourless colonies 

 are fished into dextrose broth and those organisms producing 

 acid and gas in this medium are afterwards tested in the usual 

 media for biochemical reactions and also with a specific serum 

 in low dilution. Morgan's No. 1 Bacillus invariably ferments 

 dextrose and Isevulose, and usually also arabinose and galactose, 

 with the production of acid and gas. Mannite is also usually 

 fermented but not saccharose, dulcite, maltose, dextrin, or 

 saHcin. Indol is produced in peptone water and milk becomes 

 alkaline in about ten days. Gelatine is not liquefied. 



B. Tuberculosis 



For the detection of B. tuberculosis in milk two processes 

 have been employed : (a) the microscopical and (6) the inocula- 

 tion method. 



Microscopical. In very rare cases the presence of B. tuber- 

 culosis in milk may be demonstrated by the examination of 

 stained films of the milk without previous concentration, but 

 the percentage of positive results so obtained is so small as to 

 render the process valueless for pubhc health work. When 

 the organisms are comparatively numerous they may be found 

 in the deposit obtained by centrifugalising 50 to 100 c.cms. of 

 milk at 2000 to 3000 revolutions per minute for thirty minutes. 

 For the preparation of cover-sHp films Delepine ^^ recommends 

 spreading small portions of the sediment over cover slips which, 

 when dry, are placed in a covered capsule containing equal 

 parts of absolute alcohol and ether for two hours. At the 

 expiration of this period the capsule is placed in a dish con- 



