738 A MANUAL OF BACTERIOLOGY 



about 8,000,000, and may contain as many as 30,000,000, 

 organisms per cubic centimetre. Although all the ordinary 

 species may be met with, milk has a bacterial flora largely 

 its own, comprising many forms producing lactic and 

 butyric acid fermentations. Organisms also occur having 

 more or less specific effects, and giving rise to bitter milk, 

 viscid milk, etc. The lactic ferments are mostly non- 

 sporing, the butyric chiefly sporing, species. The com- 

 monest of the lactic ferments are Streptococcus lacticus 

 (non - gas - forming) and B. acidi lactici (gas-forming), 

 which has some similarity to the colon bacillus (see 

 table, p. 450). Another common lactic organism is the 

 O'idium lactis, a mycelial form, the colonies of which 

 appear as little fluffy tufts. In addition to the organ- 

 isms named, pathogenic species may be met with viz. 

 the tubercle, diphtheria, typhoid, paratyphoid, Gartner, 

 and dysentery bacilli, and cholera vibrio, the M. meli- 

 tensis (goats' milk), M. pyogenes, and the Streptococcus 

 pyogenes. The B. coli and B. Welchii are generally 

 present in milk, and the B. lactis aerogenes is sometimes 

 found (p. 464). Scarlatina (see " Scarlatina ") and foot- 

 and-mouth disease may likewise be conveyed by milk, 

 and the diarrhoea of infants is largely due to the use of 

 milk swarming with microbes, some of which in them- 

 selves may be harmful, and which also by the products 

 they form tend to set up gastro -enteritis. The percentage 

 of samples infected with tubercle bacilli varies much : 

 Barton and Hewlett found only one out of twenty-six 

 samples taken at London railway termini. The supply 

 of the large dairy firms is also comparatively free from 

 tuberculous infection, as considerable precautions are 

 taken to exclude tuberculous animals. For the quarter 

 ending March 31, 1911, of 760 samples examined for the 

 London County Council 106, or 13-9 per cent., were 

 found to be tuberculous, and since 1907 of 5,698 samples 



