THE COLON-TYPHOID SEEIES 335 



is not digested. Upon agar plates the colonies are moist, 

 opaque, becoming darker and more coarsely granulated. 

 Gelatin is not liquefied. 



Physiology. — Bacterium coli grows readily at blood heat 

 and also at room temperature. Acid and gas are produced 

 from dextrose and lactose. The typical Bacterium coli does 

 not produce gas from sucrose but there are closely related 

 species which show this reaction. It is readily destroyed 

 by heat. The gas produced from carbohydrates is a mix- 

 ture of equal volumes of carbon dioxide and hydrogen. In 

 a suitable glucose peptone medium sufficient acid is pro- 

 duced so that methyl red is changed to a deep red color. 

 Indol is usually produced in Dunham's solution. The^ 

 Voges-Proskauer test is negative. The organism is aerobic 

 and facultative anaerobic. 



Pathogenesis. — Although Bacterium coli is* usually re- 

 garded as nonpathogenic, there is reason to suppose that 

 occasionally virulent varieties are developed which may 

 produce disease in animals, particularly the so-called calf 

 scours or calf diarrhea. 



Recognition. — The physiological and cultural characters 

 of this organism make it comparatively easy to recognize 

 when present in the water and to isolate from sewage. The 

 methods used will be discussed at greater length under the 

 heading of Bacteriology of Water and Sewage. 



Intermediate or Eistteritidis Subgroup 



Several species of bacteria belonging to this subgroup are 

 of economic importance because of their association either 

 as primary cause or secondary invaders with several dis- 

 eases of man and animals. Among them are the Bacterium 

 paratyphi and Bacterium schottmiilleri causing paratyphoid 

 fevers, the Bacterium enteritidis associated with food 

 poisoning, Bacterium morgani which has been found asso- 

 ciated with a typical dysentery in man. Bacterium pul- 



