5 2 PATHOGENIC BACTERIA. 



due, the growth of various bacteria in stale meat bring- 

 ing'about in its proteid substances the development of 

 toxic ptomaines. Kaensche 1 carefully investigated the 

 subject, and gives a synoptical table containing all the 

 bacteria of this class described. His researches show 

 that there are at least three different bacilli whose growth 

 causes the development of poisonous ptomaines in meat. 



Toxins and toxalbumins are also very common. 



3. Chromogenesis.^\MOS^ bacteria which produce col- 

 ored colonies or impart color to the medium in which 

 they grow are called chromogenic ; those with which no 

 color is associated, non-chromogenic. Most chromogenic 

 bacteria are saprophytic and non-pathogenic. Some of 

 the pathogenic forms, as the Staphylococcus pyogenes 

 aureus and citreus, are, however, color-producers. It 

 seems likely that the bacteria do not form the actual 

 pigments, but certain chromogenetic substances which, 

 uniting with substances in the culture-medium, pro- 

 duce the colors. 



Galleotti has described two kinds of pigment, one of 

 which, being soluble, readily penetrates all neighboring 

 portions of the culture-medium, like the colors of Bacillus 

 pyocyaneus, and an insoluble pigment which does not 

 tinge the solid culture-media at all, but is constantly 

 found associated with the colonies, like the pigment of 

 Bacillus prodigiosus. The pigments are found in their 

 greatest intensity near the surface of the colony. The 

 coloring matter never occupies the protoplasm of the 

 bacteria (except the Bacillus prodigiosus, in whose cells 

 occasional pigment-granules may be seen), but occurs in 

 an intercellular excrementitious substance. 



The pigments are so varied as to give almost every 

 known color. It sometimes happens that a bacterium 

 will elaborate two or more colors. The Bacillus pyo- 

 ryuneus thus produces pyocyanin and fluorescin, both 

 being soluble pigments one blue, the other green. 

 Gessanl has shown that when the Bacillus pyocyaneus 



1 Zeitsch rift fii r //I- N /.-// . etc., IJ<1. xxii., Heft I, June 25, 1896. 



