372 



THE TYPHOID BACILLUS 



FIG. 219. Typhoid bacillus. 

 Culture on potato. 



transparent : the edges of each colony become indented and sinuous, and at 

 the same time ridges extend from them into the centre, which becomes 

 thicker than the margins. These details may be made out clearly with a 

 lens. The general appearance has been compared by German writers to an 

 iceberg. 



Colonies developing in the depth of the gelatin and sometimes even those 

 on the surface have quite a different appearance. They are round and 

 opaque, and remain about the size of a pin's head. 



3. Agar : Coagulated serum. There is nothing characteristic about the 

 growth on these media. After incubating for 24 hours at 37 C. a whitish 

 streak appears, which subsequently becomes thicker and cream-coloured. 

 Glycerin-agar yields a more copious growth. 



4. Potato. The growth of the typhoid bacillus on potato is as a rule 

 characteristic. At first sight there appears to be no growth at all : but on 



illuminating the surface of the potato by day- 

 light a delicate, moist, shiny deposit like the 

 icing on cakes is seen along the line of sowing. 

 Sometimes the culture assumes a bistre tint 

 later. 



In some cases however the growth on potato 

 is plainly visible, being yellowish in colour and 

 occasionally even definitely brownish. Buchner 

 states that this appearance can be obtained at 

 will by making the potato alkaline with a solution 

 of carbonate of soda. 



5. Remy and Sugg's medium. To avoid complications induced by varia- 

 tions in the chemical composition of potato, an artificial medium has been 

 prepared by Kemy and Sugg which contains the constituent ingredients of 

 potato. According to the authors the typhoid bacillus on this medium 

 invariably gives a characteristic growth ; " a limited, absolutely colourless, 

 scalloped film." 



The medium is prepared as follows. 

 (a) Make a solution containing : 



Water, - 



Glucose, - 



Peptone, 



Asparagin, 



Citric acid, 



Neutral potassium phosphate, 



Magnesium sulphate, 



Potassium sulphate, - 



Sodium chloride, 



Carbonate of sodium q.s. to render the whole slightly alkaline. 

 (6) To 100 c.c. of this solution add : 



Gelatin (extra quality), 10 grams. 



Calcined magnesia, ---..... 2 



Distribute in tubes, sterilize, slope. Sow in stroke culture. 



8 l B ^ e r~ Sterilized ox-bile is a very useful medium on which to grow the 

 typhoid bacillus (Conradi). It is used as an " enrichment medium " for 

 obtaining [primary] cultures from material in which the bacillus is only 

 present in small numbers, as for example the blood of enteric fever patients 



7. Milk. The bacillus grows abundantly in milk without coagulating the 

 medium. 



1000 c.c. 

 20 grams. 

 5 

 5 



0-75 gram. 

 5 grams. 

 2-5 

 2-5 



1-25 ,: 



