30 ESSENTIALS OF BACTERIOLOGY 



Coagulating, fat-splitting, hydrolytic ferments are some of 

 the other varieties. 



Toxins and toxalbumins are various albuminoids pro- 

 duced in the animal organism and in culture-media which are 

 very poisonous, and are considered the prime cause of disease. 



Putrefaction. When fermentation is accompanied by 

 development of offensive gases, a decomposition occurs which 

 is called putrefaction, and this, in organic substances, is due 

 entirely to bacteria. 



Pigmentation. Some bacteria are endowed with the 

 property of forming pigments either in themselves, or pro- 

 ducing a chromogenic body which, when set free, gives rise to 

 the pigment. In some cases the pigments have been isolated 

 and many of the properties of the anilin dyes discovered in 

 them. 



Phosphorescence. Many bacteria have the power to 

 form light, giving to various objects which they inhabit a 

 characteristic glow or phosphorescence. 



Fluorescence. An iridescence, or play of colors, devel- 

 ops in some of the bacterial cultures. 



Gas-formation. Many bacteria, anaerobic ones especi- 

 ally, produce gases, noxious and odorless; in the culture- 

 media the bubbles which arise soon displace the media. 



Odors. Some germs form odors characteristic of them: 

 some are pleasant and even fragrant; others, foul and nause- 

 ous. 



Effect of Age. With age, bacteria lose their strength and 

 die. 



CHAPTER III 

 INFECTION 



How Bacteria Cause Disease. Many theories have 

 been advanced to explain the action of bacteria in causing 

 disease, but only a few of the more important ones can be 

 discussed. Nearly all the changes found in the organs of the 



