62 



ing growth, sharply defined but irregular borders and their 

 bluish appearance, especially with transmitted light. Com- 

 pare with colonies on gelatin plates made in Exercise XXIX, 



EXERCISE XXXI. 



BACII^IvUS CHOLERAE SUIS AND BACILLUS TYPHOSUS. 



§ loi. Explanatory note. The bacilli of typhoid fever 

 and of hog cholera resemble each other very closely mor- 

 phologically and in certain of their cultural characters and 

 biochemic properties. I,ike B. coli communis each of these 

 organisms has several varieties. Alreadj^ several distinct 

 varieties of the hog-cholera bacillus have been described. 

 (The hog-cholera group of Bacteria. Bulletin No. 6, U. S. 

 Bureau of Animal Industry, p. 9.) Certain of the varieties 

 of these species approach each other very closely while 

 others approach B. coli communis in their various manifesta- 

 tions. It is important, therefore, that the morphology and 

 properties of each of these species, should be carefully de- 

 termined. The fact should be kept clearly in mind that 

 while these two species and the colon bacillus resemble each 

 other in certain directions they are so far as has yet been 

 demonstrated, distinct species. The special methods of 

 differentiation must be omitted from this elementary course. 

 Read carefully the chapter on Bacillus typhosus in the text- 

 book. 



§ 102. General directions. Examine the plate cultures 

 made from the intestine for the colon bacillus. 



Determine the approximate number of colonies on each 

 plate and note especially the number of colonies of B. coli 

 communis and describe their appearance. 



Inoculate a tube of agar, one of milk, and a fermentation 

 tube of glucose bouillon from one of the colonies. Study 



