42 BIOLOGY OF BACTERIA 



peptone from albumins, the formation of kreatinin, and the change 

 of hemoglobin into methemoglobin. 



Chromogenic Bacteria. There are a number of both pathogenic and 

 numerous non-pathogenic bacteria which in their growth under 

 certain conditions form pigments of various colors. One of the 

 conditions necessary to pigment formation is the presence of mag- 

 nesium and sulphur compounds in the culture medium. Free oxygen 

 is also generally required. There are examples when free oxygen must 

 not be present, as in the case of the Spirillum rubrum, which forms 

 a red pigment only under anaerobic conditions. As a rule, the pig- 

 ment is formed better at lower temperatures than are present in 

 the incubator, and better in the dark than in the olirect or diffuse 

 sunlight. Some bacteria form a pigment only on certain culture 

 soils, as, for example, the glanders bacillus on potatoes. Some chro- 

 mogenic bacteria and the colors which they produce are: 



The Staphylococcus pyogenes aureus, a golden-yellow pigment. 



The Staphylococcus pyogenes citreus, a lemon-yellow pigment. 



The anthrax bacillus, a brown pigment. 



The glanders bacillus (on potato), a red-brown to yellowish-red 

 pigment. 



The Bacillus pyocyaneus, a green pigment. 



The Bacillus violaceus, a violet pigment. 



The Bacillus of avian tuberculosis, a yellowish-red to brown pig- 

 ment. 



The Bacillus prodigiosus, a red pigment. 



The Bacillus cyanogenus (in milk), a blue pigment. 



Some bacteria, particularly those occurring in sea water, form a 

 fluorescent or phosphorescent material. The luminosity or phos- 

 phorescence of the ocean is due to the presence of these in enormous 

 numbers. 



Fermentation and Enzymes. Bacteria and other low vegetable 

 microorganisms, such as saccharomyces (yeast cells) and moulds, 

 play an extensive role in the outside world as the cause of fermenta- 

 tive processes of organic compounds. Quite a number of soluble 

 ferments or enzymes are furnished by pathogenic bacteria, and they 

 lead to certain manifestations both in the bodies of infected animals 

 and in artificial culture media. 



The enzymes thus secreted are: diastase, the enzyme which splits 

 up starch and forms maltose (malt sugar) ; invertase, which changes 

 saccharose (a disaccharid) into glucose or grape sugar or dextrose 

 (a monosaccharid) ; rennet, which precipitates the soluble casein from 

 milk; urase, which decomposes urea; lipase, which splits the fats into 

 their component fatty acids and glycerin; and a peptonizing ferrrtent, 

 which dissolves proteids and forms, from their complicated body, 

 peptone and other simpler compounds. The action of the pepton- 

 izing ferment or enzyme can be well studied in artificial cultures pre- 

 pared from blood serum or gelatin. As the peptonizing of these 



