78 LABORATORY BACTERIOLOGY 



EXERCISE XXVIII 



BACILLUS COLI COMMUNIS AND THE PARACOLON 



117. Work for this exercise. Reexamine the cultures of 

 B. coli communis and note any changes which have occurred 

 in their appearance; Determine the gas formula in the fer- 

 mentation tubes with the different sugars. Place the milk and 

 litmus-milk cultures in the incubator and examine them later. 



Examine carefully and describe the cultures of the paracolon 

 bacillus. Examine microscopically at least one culture. Note 

 especially its motility. 



Examine and describe fully the colonies on the gelatin plates. 

 Preserve the plates and examine them at the following exercises. 



Examine microscopically, in a stained preparation, the bac- 

 teria from a colony on the gelatin plate. Preserve a prepara- 

 tion to accompany the notes. 



Isolate B. coli communis from the intestine of an animal. 

 The intestine will be furnished. 



Inoculate with B. cholera, suis, for Exercise XXIX, a tube 

 of each medium in Groups A and D, and similar tubes with 

 B. typhosus, from the cultures furnished. 



118. Isolating B. coli communis from the intestine. Care- 

 fully open the intestine by a longitudinal incision. Scrape 

 away the contents, if any, from a small area of the mucous 

 membrane. Take a loopful of the mucus from the surface of 

 the mucous membrane and inoculate a large tube of liquefied 

 gelatin with it. After shaking the tube carefully, inoculate a 

 second tube with 2 loopfuls from the first, and a third with 3 

 loopfuls from the second. Pour the gelatin into Petri dishes 

 and label them. These plates should be examined daily. 

 The colonies of B. coli communis can be distinguished from 

 others which may appear by their thin spreading growth, 

 sharply defined but irregular borders, and their bluish appear- 

 ance, especially with transmitted light. Compare with colo- 

 nies on gelatin plates from a pure culture (Exercise XXVII). 



