134 BIOLOGY AND TECHNIQUE 



mercial agar varies considerably. The preparation of the medium is 

 as follows: 



Dissolve 4.5 gms. of dry agar in 500 c.c. of distilled water over a 

 free flame, making up for loss by evaporation. In another vessel 10 

 gms. of pepton, 5 gms. of beef extract, and 8.5 gms. of salt are dis- 

 solved in 500 c.c. of distilled water. This may be heated until com- 

 plete solution has taken place and the loss by evaporation made up. 



The two solutions are then mixed and heated for thirty minutes; 

 loss by evaporation is then made up with distilled water and the solu- 

 tion is filtered through cotton until clear. The reaction is then adjusted 

 to one per cent acidity and the medium tubed — 10 c.c. to each tube. 

 Sterilize in autoclave, cool, and store in ice chest. 



The typhoid bacillus is characteristic on the Hesse medium only 

 when the dilution poured in the plates is so high that only a few colonies 

 appear. The typhoid colonies are much larger than are the colon colonies 

 and may often be several centimeters in diameter. 



Piorkowski's Urine Gelatin.^ — ^Normal urine of a specific gravity of 

 about 1.020 is collected for several days. At the end of this time, when 

 its reaction has become alkaline, pepton 5 per cent and gelatin 3.3 

 per cent are added. This mixture is heated upon a water bath for one 

 hour, filtered, and tubed. The tubes are sterilized by the fractional 

 method. 



In using this medium for the isolation of typhoid bacilli from the 

 feces, two loopfuls of feces are placed into a tube of the melted urine 

 gelatin, and from this dilutions are made into other tubes, taking four 

 loopfuls from the first into the second and six to eight from the second 

 to the third. Plates are then poured and kept at about 20° C. The 

 typhoid colonies show fine processes or filaments, while the colon 

 colonies are quite compact. 



Capaldi's Medium.^ — The composition of this medium is as follows: 



Distilled water 1,000 c.c. 



Pepton (Witte) 20 gms. 



Gelatin 10 



Agar 20 



Dextrose (or preferably mannit) 10 



NaCl 5 



KCl 5 



It is advisable to dissolve the agar in 500 c.c. of water, making up 



' Piorkowski, Deut. med. Woch., vol. 25, 1899. 

 2 CapaUii, Zeit. f. Hyg., xxiii, 1896. 



