90 BACTERIOLOGICAL EXAMINATION OF WATER. 



Proskauer and Capaldi, No. I. After twenty-four hours incu- 

 bation at 37 C. there is a growth, and the medium is rendered 

 strongly acid. 



Proskauer and Capaldi, No. II. After twenty-four hours incu- 

 bation at 37 C. there is a growth, and the reaction of the 

 medium is either unchanged or rendered slightly alkaline. 



Glucose- and Lactose-broth. After twenty-four hours incuba- 

 tion at 37 C. there is marked growth, and bubbles of gas form 

 on the surface. 



Microscopical Characters. It usually appears as a very short 

 bacillus, often strongly resembling a coccus ; but longer forms 

 are frequently seen especially in old cultures. As regards 

 motility it varies considerably ; sometimes it is almost motion- 

 less, at other times it appears to be as motile as the B. typhosus. 

 As a rule it possesses from one to three flagella, which are very 

 brittle and difficult to stain ; occasionally eight to twelve long- 

 wavy flagella are present. It does not form spores. 



Staining Reactions. Stains readily with basic dyes; it is 

 decolourised by Gram's method. 



Reactions to Specific Sera. It is not agglutinated by highly 

 dilute anti-typhoid serum. 



The above description gives the chief characteristics of the 

 typical B. coli ; but when studies are made of sewage and stools 

 derived from human beings many varieties are found which do 

 not conform to the type. The most common varieties are the 

 following : 



(1) The colonies exactly resemble the type ; gas is produced 

 in sugar media and indol formed in peptone ; but milk is not 

 coagulated, though the amount of acid produced in litmus- whey 

 may be considerable. 



(2) The colonies are typical ; gas is produced in sugar media; 

 milk is coagulated ; but indol is not formed in peptone solution. 



(3) The colonies are typical ; gas is produced in sugar media ; 

 but indol is not formed and milk is not coagulated. 



(4) The colonies are typical ; but there is no coagulation of 

 milk, production of gas, nor formation of indol. 



(5) The colonies are typical ; indol is produced in peptone 

 solution ; but there is no formation of gas in glucose media nor 

 coagulation of milk. 



