484 BACTERIOLOGIC TECHNIC. 



10 gm. peptone, 5 gm. sodium chlorid. It is warmed in the steam 

 chamber until all is melted, then neutralized with normal sodium 

 hydroxid, filtered, and sterilized. After the liquefied gelatin is filled 

 into tubes, it is again sterilized. 



( b ) Meat infusion gelatin : The same as a, but without the addition 

 of peptone and sodium chlorid. 



(c) Beer-wort gelatin: Is obtained by the addition of 10% gelatin to 

 the wort. It is not neutralized. 



(d) Plum decoction gelatin: 500 gm. of dried plums are boiled in 

 500 c.c. of water ; the fluid is then poured off, and the plums agaia 

 boiled in 500 c.c. of water. Both fluids are then mixed, filtered, and 

 10% gelatin added. It is not neutralized. 



(e) Herring gelatin: Two salt herrings, unwashed, are boiled in 1 

 liter of water, and to the filtrate 10 % gelatin is added. It is not neu- 

 tralized. 



(/) Potato-water gelatin: according to Holz, for Bact. typhi : 500 

 gm. of potatoes are carefully washed, peeled, finely grated, and 

 squeezed through a linen cloth. The turbid juice may be allowed to 

 settle for twenty-four hours and is then filtered, or, as we always do, 

 it may be filtered at once through animal charcoal, and, after heating, 

 if necessary the filtration is repeated. After heating for an hour in the 

 steam chamber, 10% gelatin is added to the clear fluid, when it is 

 again heated in the steam chamber, filtered, filled into tubes, and 

 sterilized on three successive days. It is not neutralized. (H. K. 

 Lang.) 



(g) Potassium iodid potato-water gelatin (Eisner) : 1% potassium iod id 

 is added to prepared gelatin. This is best done by adding the required 

 amount of strong sterilized solution to prepared gelatin just before 

 using it. 



g. Nutrient Agar. — To 1000 c.c. of meat infusion 10 gm. of fine cut 

 agar are added and the mixture is boiled in a glass flask over an open 

 fire for one hour until the solution is complete; then the evaporated 

 water is replaced and 10 gm. peptone and 5 gm. sodium chlorid are 

 added. After again heating in the steam chamber the fluid is neutral- 

 ized and filtered by means of the hot-water funnel, filled into tubes, 

 and sterilized. 



io. To obtain grape- or milk-sugar agar, 2% of either substance 

 is added simultaneously with the peptone and salt. Since meat-infu- 

 sion agar usually contains traces of grape-sugar, we have for some time 

 prepared a milk-sugar agar which is free from grape-sugar according 

 to the method described under A. 



ii. Glycerin-agar. — To the prepared nutrient agar 5% of glycerin 

 is added, when it is filled into tubes and sterilized. 



12. Sugar-chalk Agar. — Usually finely pulverized, dry, sterilized 

 carbonate of calcium is added to liquefied sugar-agar in sufficient quan- 

 tity to render it cloudy and opaque. It is then inoculated with the 

 bacteria and poured into plates. 



13. Potatoes. — After thorough washing and rinsing the potatoes 

 are peeled, cut into slices 1 cm. thick, and sterilized several times in 

 deep Petri dishes. The peeled potatoes may also be perforated with a 

 large cork borer and the cylinders be divided by an oblique cut into 



