46 



DAIRY BACTERIOLOGY 



Bacterium vulgar e (Fig. 28), which coagulates and peptonises milk ; 

 it can grow at low temperatures. Many closely related forms are 

 pathogenic. The ptomaine poisons produced in meat are generally 

 due to certain proteus and coli bacteria. The proteus group 

 includes several colour-producing bacteria, such as the Bacterium 

 synxantum of yellow milk and Bacterium erythrogenes of red milk. 

 The latter, however, differs from the other proteus bacteria in 

 being non-motile. Bacterium prodigiosum, which produces a fine 

 red colour, especially when grown on starchy media, is far commoner 

 of occurrence than the two last- mentioned organisms ; this 



FIG. 48. Bacillus subtilis. (After Miyula.) a. Active rods before spore 

 formation, d. Stained to show the flagellse. c. Rods with spores. All 

 these X 1,000. b. A piece of film. X 100. 



phenomenon was formerly taken for the appearance of blood on 

 the Host. As the red colouring matter is not soluble in water, 

 the bacterium cannot colour milk red, but can only form red spots 

 on the cream layer. It is Gram-negative, and most varieties 

 coagulate milk quickly by forming both acid and rennet. The 

 author has shown that it hydrolyses fat as actively as Bacterium 

 fluorescens liquefaciens. 



5. The Hay and Potato Bacteria. These organisms are distin- 

 guished by their ability to form spores which are more resistant to 

 heat than those formed by the butyric acid bacteria. They are 

 only killed after three to six hours' boiling, and a few species which 

 do not grow at ordinary temperatures form spores capable of 



