EXPERIMENTS. 321 



the same channels through which the typhoid bacillus 

 gains access to this viscns are likewise open to other 

 organisms present in the intestines, and for this reason 

 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 that of 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 

 organisms look as if they contained spores? How 

 would you demonstrate that the vacuolations are not 

 spores ? 



Obtain from the normal faeces 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? 



