34 BACTERIOLOGY. 



cocci are frequently present, but do no harm unless the 

 vitality is lowered. The stomach is generally free 

 from, bacteria, due to the acid in its secretions. If 

 however there is any disturbance of digestion and the 

 secretions are no longer acid, the bacteria swallowed 

 in the food may cause fermentation and other dis- 

 orders. The intestine harbors great numbers of bac- 

 teria, chiefly the colon bacillus* and others closely 

 allied to it. They are, in health, not only harmless, 

 but of much benefit in breaking down the food into 

 substances that can be absorbed for nutriment of the 

 tissues. Under conditions of lowered resistance or 

 when injury to the intestines has been done, they may 

 cause infection. 



After infection has taken place it may remain 

 localized in the form of a boil or abscess, or it may 

 spread so that the blood contains the infecting organ- 

 ism. When infections become generalized the condi- 

 tion is called septicemia, and when there is added to 

 this scattered areas of pus formation throughout the 

 body the condition is called pyemia. Toxemia is the 

 condition caused by the poisons of bacteria, either in 

 local or general infections. 



How do bacteria produce injury to the tissues? 

 In two ways: The multiplication of bacteria in the 

 tissues may cause injury in a mechanical way by 

 obstructing the very small blood-vessels, causing the 

 necrosis or death of the tissue. The absorption of the 

 necrotic material gives rise to the symptoms of infec- 

 tion. Much greater injury is produced by the absorp- 



