ISOLATION OF SPECIFIC PATHOGENES 78c 



typhoid organisms. Another principle is involved in 

 the media proposed by Hiss and Hesse. These are 

 both agar media of lower spissitude than ordinary 

 agar and the separation of the typhoid and colon groups 

 of organisms depends on the greater motility of the 

 former and their tendency to swim out from the colonies 

 and form branch-like processes or turbid zones on a 

 semi-soUd medium. The Hiss medium is made up as 

 follows (Hiss, 1902): 



Agar 15 gm. 



Gelatin 15 gm. 



Liebig's meat extract 5 gm. 



NaCl 5 gm. 



Dextrose 10 gm. 



Distilled water icxdo cc. 



Reaction i per cent normal. 



The Hesse medium has been used with great success 

 by Jackson and Melia (1909). Its general composition 

 is as follows: 



Agar 5gm. 



Witte's pepton 10 gm. 



Liebig's meat extract 5 gm. 



NaCl 8.5 gm. 



Distilled water 1000 cc. 



Reaction i per cent normal. 



Jackson (1909) reconmiends that the agar used 

 should be dried for half an hour at 105°, and under 



