THE PREPARATION OF CULTURE MEDIA 133 



The agar is thoroughly dissolved in 1,000 c.c. of distilled water. When 

 the agar is melted, the gelatin, meat extract, and salt are added and dis- 

 solved by further heating. Any loss in weight is then adjusted by the 

 addition of water. No titration or adjustment of reaction is necessary. 

 The medium should be cleared with the whites of two eggs, and filtered 

 through cotton. To the cleared medium is added one per cent of 

 dextrose, and the medium tubed, about 8 c.c. to each tube, and sterilized. 

 Hiss' Tube Medium. — The composition is as follows: 



Agar 5 gms. 



Gelatin 80 " 



Liebig's meat extract 5 " 



Sodium chloride 5 " 



Dextrose 10 " 



Distilled water 1,000 c.c. 



The method of preparation is the same as for the plating medium. 

 The agar is thoroughly dissolved, and then the gelatin, meat extract, 

 and salt are added and dissolved. After adjusting the loss in weight, 

 the volume should be determined, a careful titration made, and the re- 

 action adjusted to one and five-tenths per cent acid by the addition of 

 f- HCl solution. The medium is then cleared with the whites of eggs, 

 filtered, and one per cent dextrose added. It is then tubed and sterilized. 



Hesse's Medium.' — The medium devised by Hesse for typhoid-colon 

 differentiation depends for its usefulness, as does the Hiss tube medium, 

 upon the great motility of the typhoid bacillus. It may be used directly 

 for the examination of feces or, as suggested by Jackson and Melia,^ 

 after preliminary enrichment of the material to be examined by the 

 use of the lactose-bile medium of Jackson. (See p. 138.) 



The Hesse medium is made up as follows: 



Agar 5 gms. (4 . 5 gms. absolutely dry.) 



Pepton (Witte) 10 " 



Liebig's beef extract 5 " 



Sodium chloride 8.5 " 



Distilled water l,000c.c. 



Jackson and Melia, in studying this medium, have found that 

 complete drying of the agar and the use of 4.5 gms. of this dried prepara- 

 tion give more uniform results, since the amount of moisture in com- 



I Hesse, Zeit. f. Hyg., Iviii, 1908. 



' Jackson and Melia, Jour, of Inf. Dis., vi, 1909. 



