TYPHOID INOCULATION IN ANIMALS. 231 



even here the bacterium coli communis, the normal 

 organism of the colon, is not unlikely to be found. This 

 organism, however, always grows visibly on potato, co- 

 agulates milk, produces a more pronounced pink color in 

 litmus-milk than does the typhoid bacillus, and is much 

 less actively motile. 



Obtain a pure culture of typhoid bacilli and from 

 this make inoculations upon a series of potatoes of dif- 

 ferent age and from different sources. Do they all grow 

 alike ? 



Make a series of twelve tubes of peptone solution to 

 which rosolic acid has been added. Inoculate them all 

 with as near the same amount of material as possible 

 (one loopful from a bouillon culture into each tube) ; 

 place them all in the incubator. Is the color-change, as 

 compared with the control tube, the same in all cases? 



Compare the morphology of cultures of the same age 

 on gelatin, agar-agar, and potato. 



Select a culture in which the vacuolations are quite 

 marked. Examine this culture unstained. Do the or- 

 ganisms look as if they contained spores ? How would 

 you demonstrate that the vacuolations are not spores ? 



Obtain from the normal feces a pure culture of the 

 commonest organism present. Write a full description 

 of it. Now make parallel cultures of this organism and 

 of the typhoid organism on all the different media. How 

 do they differ ? In what respects are they similar ? 



