182 ATLAS OF BACTERIOLOGY. 



Both fluids are then mixed, filtered, and ten per cent 

 gelatin is added. Not to be neutralized. 



(e) Herring gelatin. Two salt herring, unwashed, 

 are boiled in 1,000 gm. water and ten per cent gelatin 

 is added to the filtrate ; not to be neutralized. 



(/) Potato-water gelatin, according to Holz, for 

 bacterium typhi: 500 gm. potatoes are thoroughly 

 washed, peeled, finely grated, and squeezed through 

 a linen cloth. The opaque juice may be allowed to 

 settle for twenty-four hours and then filtered, or, as 

 we always prefer, filtered at once through pure 

 animal charcoal. After heating one hour in the 

 steam chamber ten per cent gelatin is added to the 

 clear fluid, this is again heated in the steam chamber, 

 filtered, poured into test tubes and sterilized on three 

 successive days. 



(g) Potassium iodide potato-water gelatin (Eisner) : 

 One per cent iodide is added to the gelatin. The 

 best way is to add a well-sterilized solution in the 

 requisite amounts to gelatin which has just been 

 made ready for use. 



9. Nutrient agar. To 1,000 gm. bouillon add 

 10 gm. very finely divided agar, boil for one hour 

 on the fire in a glass retort until completely dis- 

 solved; the water which has evaporated is replaced 

 and then 10 gm. peptone and 5 gm. sodium chloride 

 are added. After heating again in the steam cham- 

 ber the fluid is neutralized, filtered by means of the 

 hot- water funnel, placed in test tubes, and again 

 sterilized. 



10. In order to make grape-sugar or milk-sugar 

 agar, two per cent of the corresponding substance is 

 added with the peptone and sodium chloride. As 



