MILK AND THE PUBLIC HEALTH CHAP. 



the characters most used in earlier bacteriological investiga- 

 tions, such as morphology, pigment-production, characters of 

 the gelatine plate colonies, growth in broth, milk, potato, etc. 

 Other workers place in addition to, or in substitution for, these 

 tests, great reliance upon pathogenicity, agglutination tests, or 

 the haemolytic tests introduced by Schottmuller. A further 

 group of workers base their differentiating characters in large 

 part upon the ability of streptococci to produce acid in certain 

 sugars or alcohols. 



It cannot be said that any one series of tests are satisfactory 

 or sufficient, but the writer and others have found from 

 extensive experience with milk streptococci that the sugar- 

 alcohol tests, together with morphology, growth in broth and 

 milk, and pathogenicity, are of most utility. 



Houston 1 studied the biological characters of 172 strep- 

 tococci isolated from various samples of milk. Using the 

 sugar -alcohol tests he found that they differentiated the 

 streptococci into a very large number of groups. He could 

 by these tests, and apart from morphology and growth in broth, 

 divide them into no less than 38 different groups, of which 

 only one group contained more than 12 per cent of the isolated 

 organisms. Houston found that the streptococci of milk differ 

 somewhat from the streptococci of cow-dung and human faeces. 

 This is brought out by the following table, to which is added 

 the results of 71 streptococci isolated by the writer' 2 from 

 milk drawn direct from the udder and teats of healthy cows : 



1 Report to London County Council, 1905. 

 Report of Medical Officer, Local Government Board, 1906-7, p. 205. 



