304 BACTERIOLO&Y. 



the bacterium coli commune, a normal inhabitant of 

 the colon, may also be found in this locality. 



Note. — Obtain a pure culture of typhoid bacilli, and 

 from this make inoculations upon a series of potatoes of 

 different age and from different sources. Do they all 

 grow alike ? 



Before sterilizing, render another lot of potatoes 

 slightly acid with a few drops of very dilute acetic 

 acid ; render others very slightly alkaline with dilute 

 caustic soda. Do any differences in the growth result ? 



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 ? 



Bacterium Coli Commune (colon bacillus ; baciUus 

 Neapolitanus of Emmerich). — This organism was found 

 by Escherich, in 1885, in the intestinal discharges of 

 milk-fed infants. It has since been demonstrated to 



