THE BACILLUS OF TYPHOID FEVER. 445 
Several test tubes, each of which contains ten cubic centimetres 
of neutral, sterilized bouillon, are used in the experiment. From 
three to nine drops of the acid solution are added to each of these, 
and the tubes are then placed in an incubating oven for twenty-four 
hours to ascertain whether they are still sterile after this addition. 
If the bouillon remains clear, from one to ten drops of the suspected 
water are added to each tube and they are returned to the incubating 
oven. If at the end of twenty-four hours the bouillon becomes 
clouded, this is due, according to Parietti, to the presence of the 
typhoid bacillus, which is then to be obtained in pure cultures by the 
plate method. 
The following method, suggested by Hazen and White, has been 
tested with favorable results by Foote. This method depends upon 
the fact that most of the common water bacilli do not grow at a tem- 
perature of 40° C., whereas this is a favorable temperature for the 
development of the typhoid bacillus. A small quantity of the sus- 
pected water is added to liquefied nutrient agar in test tubes, and 
plates are made. ‘These are placed in an incubating oven at 40° C., 
and the typhoid bacillus, if present, will develop colonies within two 
or threedays. At the ordinary room temperature the more numerous 
water bacilli would develop upon the same plates so abundantly that 
it would be difficult to recognize colonies of the typhoid bacillus. 
Theobald Smith (Centralb. f. Bakteriol., Bd. xii., page 367), 
has shown that the typhoid bacillus may be differentiated from other 
similar bacilli (Bacillus coli communis, bacillus of hog cholera, etc.) 
by the fact that it does not produce gas in culture media containing 
sugar—grape sugar, cane sugar, or milk sugar. The medium recom- 
mended by Smith for making this test is a peptone-bouillon contain- 
ing two per cent of grape sugar and made slightly alkaline with 
carbonate of soda. The liquid becomes clouded throughout at the 
end of twenty-four hours, but not a trace of gas is developed even 
after several days. On the other hand, the colon bacillus and other 
bacilli which closely resemble the typhoid bacillus cause an abundant 
development of gas in this medium. 
The method of Wurtz will be found useful in the detection of 
colonies of the typhoid bacillus in plate cultures from contaminated 
water, etc. This consists in the addition to the nutrient medium of 
lactose (two per cent) and a solution of litmus. When the colonies 
develop in plates made from this medium the typhoid colonies re- 
main blue, while colonies of the “colon bacillus” have a red color, on 
account of the development of lactic acid. 
Schild (1894) uses a bouillon containing formalin (1:7,000) and 
claims that the typhoid bacillus fails to grow in this medium, while 
