72 LABORATORY BACTERIOLOGY 



EXERCISE XXXII 



BACILLUS COLI COMMUNIS 



114. Of the bacteria normally present on the mucous mem- 

 branes of the animal body the colon group is, on account of 

 its Close morphological relationship to the bacilli of typhoid 

 fever and hog cholera, of more than ordinary interest. There 

 are varieties of this organism which approximate very closely 

 in their biochemic properties as well as in their morphology to 

 the typhoid and also to the hog-cholera bacilli. It is impor- 

 tant that this existing variation be recognized, and that the list 

 of properties which characterize B. coli communis should be 

 clearly determined. The differentiation of the colon and 

 typhoid bacilli, as they exist in nature, is one of the difficult 

 problems in practical bacteriological work. The culture as- 

 signed approaches very closely to the typical species. 



References. — Chapters on this organism in the text-books, 

 T. Smith, The Am. Jour, of Med. Sci., Sept., 1896. Adelaide W. 

 Peckham, Jour, of Exp. Med., Vol. II. (1897), p. 549. Adami, Ibid., 

 Vol. IV. (1899), p. 349. 



115. Work for this Exercise — Describe the appearance of 

 each of the cultures of B. coli communis made in Exercise 

 XXXI. 



Examine the bacteria in a hanging-drop preparation from 

 the bouillon and glucose bouillon cultures. 



Make and stain with carbol fuchsin a cover-glass preparation 

 from the agar culture. Measure a few of the bacilli and record 

 their size in the notes. 



Note especially the quantity of gas formed in each of the 

 fermentation tubes. These cultures should be kept until the 

 next exercise, when they should be examined again. If the gas 

 formation is then completed, determine the quantity of gas and 

 the ratio of the CO2 to the H in the gas in each tube. 



