THE COLON-TYPHOID GROUP 91 



on gelatin. Gram-staining negative.' Prescott and Wins- 

 low doubt there to be ' sufficient evidence to warrant 

 making the esculin reaction a general criterion of the 

 colon group,' and they desire to reduce the test to positive 

 reactions in a lactose fermentation medium, growth on 

 an aerobic agar streak, and microscopic examination. 



Clemesha and Houston have independently shown that 

 with fresh faecal pollution in water most of the organisms 

 fermenting dextrose ferment lactose as well, while in 

 stored or filtered water dextrose -fermenting lactose- 

 negative forms relatively increase. 



To obtain presumptive evidence of the presence of the 

 colon bacillus a medium containing a suitable carbohydrate 

 and some substance to inhibit the growth of other organ-, 

 isms is used, such as MacConkey's litmus lactose bile- 

 salt peptone-water, which is fermented with the pro- 

 duction, of acid and gas. This medium is used for further 

 work (see p. 230). 



If the organism be present in large numbers and vigor- 

 ous condition, acid and gas production will be evident 

 in less than twenty-four hours, but attenuated organisms 

 may require three days' incubation at blood-heat or at 

 a slightly higher temperature. Bile-salt has the dis- 

 advantage of suppressing some of the weak coliform 

 organisms. In examinations for faecal contamination this 

 is not a matter for worry, as feeble vigour cateris paribus 

 denotes remoter faecal ancestry, and the attribution of 

 slighter significance to their presence and numbers. (It 

 may be mentioned here that the best ' pick-me-up ' 

 media for rejuvenating sveak bacteria are liver broth, and 

 gelatin at blood-heat.) 



Pathogenesis. While in the intestine, the colon bacillus 

 is supposed by some to suppress the growth of less desir- 

 able organisms, and thus to protect the body. This 

 surmise is based on the diminution in number or absence 

 of the colon bacillus from the faeces in some bacterial 

 diseases affecting the intestines. Although chiefly of 

 importance as an ' indicator ' of pollution with excrement, 

 the colon bacillus is also capable of causing disease. The 

 organism is pyogenic, is commonly the cause of cystitis, 

 and may affect the gall-bladder and bile ducts and other 

 organs. Sir Almroth Wright suggests it may sometimes 

 be responsible for mucous colitis. Arnold Lawson 



