2O6 AGRICULTURAL BACTERIOLOGY. 



show themselves in the milk when freshly drawn but appeal- 

 after some hours. Red milk due to bacteria is, however, very 

 unusual. Several species of microorganisms have been found 

 with this property, the best known being />. crythrogcncs, a 

 species found by many bacteriologists both in this country 

 and Europe. This species acts so slowly that it is of no 

 practical significance in dairying. When allowed to act fully 

 on milk it makes it blood red. Several other species have 

 been described as a cause of red milk. B. prodigiosus, the 

 cause of the so-called "bleeding bread," is said occasionally 

 to produce a red color in milk, especially at its surface. 

 Menme has described a Sarcina which produced such a trouble 

 in Rendsburg, Germany. But, while it is common to find old 

 milk showing patches of red due to bacterial growth, an infec- 

 tion of red milk is rare, and the trouble is practically unknown 

 to the milk dealer. It is an experimental rather than a prac- 

 tical fermentation. 



Yellow Milk, Green Milk, etc. Other pigments are occasion- 

 ally produced in milk. Indeed, milk is such a good medium 

 for bacterial growth that almost any saprophytic bacterium may 

 develop in the milk if opportunity occurs, and pigment-form- 

 ing bacteria will be sure to produce their pigments in milk. 

 Orange-colored milk, green milk\ yellow milk, mnbcr-colorcd 

 milk, indigo milk have all been described by bacteriologists 

 as well as chocolate milk and black milk. In each case the 

 pigment has been produced by bacteria which the bacteriolo- 

 gists have isolated and studied. But these various pigments 

 are produced in milk only when the specific bacterium is grow- 

 ing in the milk by itself and not contending with the ordinary 

 milk bacteria. The pigments commonly appear after many 

 days' growth, and do not develop when the milk is filled with 

 the lactic bacteria. These various ptgmented milks are there- 

 fore simply experimental but not normal infections. In ordi- 

 nary dairying they do not occur, and are, at present, of interest 



