ISOLATING THE TYPHOID BACILLUS. 431 



bacillus causes the color to become yellow, while the 

 normal red color is not affected by the typhoid bacillus. 



The spleen of a patient dead of typhoid fever is the 

 most reliable source from which to obtain cultures of 

 the typhoid bacillus for study. But it must always be 

 remembered that the same channels through which the 

 typhoid bacillus gains access to this viscus are like- 

 wise open to other organisms present in the intestines, 

 and for this reason baotei'ium eoli 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 ages 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. 

 Are any differences in the growths noticeable ? 



Make a series of twelve tubes of peptone solution to 

 which rosolic acid has been added. Inoculate them all 

 with as nearly 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 eases. 



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 



