PREPARATION OF MEDIA 95 



Nutrient starch- jelly for study of diastasic action. 1 

 One gram of starch is rubbed up with a sterile glass rod 

 in 10 cc. of the sterile nutrient fluid (Uschinsky's solution) 

 placed in a slanting position, in test tubes, and solidified in 

 a blood-serum oven or in the top of a steamer with the vents 

 left open. There should be several heatings of two hours 

 each to insure sterilization. The temperature should not ex- 

 ceed 93 C. nor fall much below 85 C. Sterilization is ren- 

 dered much easier if the starch is prepared in a cleanly way. 

 The only difficulty experienced is in the formation of a thin 

 film of semiopaque solidified starch on the walls of the tubes 

 above the slant. This often cracks off, however, during the 

 heatings, and is largely obviated by placing the tubes in a 

 slanting position before the starch is rubbed up in the fluid, 

 taking care to soil the walls above the slant surface as little 

 as possible during the operation. 



Hiss 's medium for differentiating colon-typhoid colonies. 

 Plate culture. The composition of this medium is as 

 follows : 



Agar 15 grams 



Gelatin 15 grams 



Liebig's meat extract 5 grams 



Sodium chloride 5 grams 



Dextrose 10 grams 



Distilled water 1000 cc. 



The agar is thoroughly dissolved in 1,000 cc. of distilled 

 water, either over a free flame or in the autoclave. When 

 the agar is melted, the gelatin, meat extract and salt are 

 added and dissolved by further heating. Any loss in weight 

 is then adjusted by the addition of water. No titration or 

 adjustment is necessary. The medium should be cleared, in 

 the usual way, with the white of two eggs, and filtered 

 through cotton. To the cleared medium is added one per 

 cent of dextrose, and the medium tubed, about 8 cc. to each 

 tube, and sterilized. 



1 See Proc. Am. Asso. Adv. Sci., 1898, p. 411, or Centralb. f. Bakt., 

 Bd. V, p. 102. 



