8 GENERAL CONSIDERATIONS 



It should, however, be stated that several investigators have 

 questioned the reliability and value of these sugar-alcohol tests 

 and have not found them to be sufficiently stable. 



These tests were introduced by Gordon 1 and included the 

 following nine tests : Litmus milk for clot (three days at 37 C.), 

 reduction of neutral red broth during anaerobic incubation for 

 two days at 37 C., production of acid in three days at 37 C. in 

 slightly alkaline broth containing respectively I per cent, of 

 saccharose or lactose, raffinose, inulin, salicin, coniferin, or 

 mannite. With the exception of the use of coniferin these tests 

 have been extensively employed. 



Houston in 1902 studied the biological characters of 300 

 human faecal streptococci 2 , in 1903 the characters of 100 

 streptococci from cow-dung 3 , and in 1908 he investigated the 

 characters of 100 streptococci isolated from lumps of faeces 

 taken at a sewage outfall works 4 . 



These 500 streptococci showed the following percentage 

 positive reactions: 



Human 



Test Faeces Cow-dung "Sewage" 



Salicin 927 93 97 



Saccharose 86-3 89 49 



Lactose ... ... ... 76^3 85 ico 



Litmus milk ... ... 617 73 ico 



Neutral red broth /.. 39*3 o 



Raffinose ... ... ... 32 74 ico 



Mannite ... ... ... 24*3 o 4 



Inulin 47 13 



The biological characters of streptococci from excreta have 

 also been studied by Winslow and Palmer 5 . They examined 

 302 streptococci, 116 from human, 100 from horse, 86 from cow 

 excreta. They employed similar methods but the amount of 

 acid was in each case estimated by titration, using phenol- 

 phthalein as indicator. Each culture was incubated 72 hours at 



1 Local Government Board, Medical Officers Report, 1903-4, p. 388. 



2 Ibid. 1903-4, p. 484. 



3 Ibid. 1904-5, p. 326. 



4 Metropolitan Water Board, Fifth Research Report* 

 6 Jonrn. of Inf. Diseases, 1910, vol. vn, p. i. 



