444 THE BACILLUS OF TYPHOID FEVER. 
cultures appear to bedue. White mice and guinea-pigs usually die 
in from twenty-four to forty-eight hours when inoculated in the 
cavity of the abdomen with a virulent culture of the typhoid bacillus 
—0.1 cubic centimetre to 0.5 cubic centimetre of a bouillon culture 
three days old. According to Kitasato, the virulence of cultures 
from different cases of typhoid fever varies considerably. 
Detection of the Typhoid Bacillus in Water.—The generally 
recognized fact that typhoid fever is usually contracted by drink- 
ing water contaminated by the typhoid bacillus has led to numer- 
ous researches having for their object the discovery of a reliable 
method of detecting this bacillus when present in water in compara- 
tively small numbers in association with the ordinary water bacilli. 
The use of Koch’s plate method, as commonly employed, will 
not suffice, because the water bacilli present grow more rapidly 
and cause liquefaction of the gelatin before visible colonies of the 
typhoid bacillus are formed ; and, owing to the relatively small 
number of typhoid bacilli, these are likely to escape detection. The 
aim of bacteriologists has, therefore, been to restrain the growth of 
these common water bacilli by some agent which does not at the 
same time prevent the development of the typhoid bacillus. Chan- 
temesse and Widal were the first to propose the use of carbolic acid 
for this purpose. They recommended the addition of 0.25 per cent 
of this agent to nutrient gelatin ; but, according to Kitasato, the de 
velopment of the typhoid bacillus is restrained by an amount exceed- 
ing 0.20 per cent. 
Holz prepares an acid medium by adding gelatin (ten per cent) to 
the juice of raw potatoes, and asserts that while the typhoid bacillus 
grows luxuriantly in this medium, many other bacilli fail to develop 
init. The test is said to be still more reliable if 0.05 per cent of car- 
bolic acid is added to the “‘ potato-gelatin.” According to Holz, the 
addition of more than 0.1 per cent of carbolic acid to nutrient gelatin 
prevents the free development of the typhoid bacillus. 
Thoinot has claimed to be able to obtain the typhoid bacillus from 
mixed cultures—as, for example, from feeces—by suspending a small 
amount of material containing it for several hours in a solution con- 
taining 0.25 per cent of carbolic acid. While other bacilli are 
destroyed, the typhoid bacillus is said to survive such exposure. 
The method of Partettt has been tested in a practical way by 
Kamen, and proved to be satisfactory for the detection of the typhoid 
bacillus in water which was supposed to be the source of a local 
epidemic of the disease. The following solution is used: 
Carbolic acid, ; - : . é : - 5 grammes, 
Hy drochloric acid (pure), : : . : 4 “ 
Distilled water, . 3 : ‘ : ‘ . 100 ae 
