DETECTION OF B. TYPHOSUS IN INFECTED MATERIAL 
B. typhosus was the first to reach the surface in every case. On some of the 
plates a tew colonies of B. coli were also present. 
This seemed a promising line of investigation, and it was sought to still 
further simplify the procedure. One point in particular was encouraging ; after 
keeping the tubes for some days there was no apparent diminution in the relative 
number of typhoid bacilli present in the fluid. This was contrary to what one had 
been led to believe previously, and was probably due to the fact that the medium 
was sugar-free, or practically so, making it impossible for B. coli to produce acid in it. 
Experiment 2. 20 per cent. Gelatin 
Artificial mixtures of typhoid and colon bacilli were prepared as before, and 
amounts varying from o - 1 c.c. to 1 "O c.c. were introduced into the bottom of each 
of twelve sterile tubes ; 5 c.c. of 20 per cent, gelatin was then added to each tube 
and allowed to harden. Thus the capsules were done away with. After the 
hardening of the gelatin, 1 5 c.c. of bile-salt gelatin were introduced into six, and 
25 c.c. into the other six, of the tubes, as before. Cultures were made from the 
surface at once, and after placing the tubes in the thermostat, at intervals of one 
hour, the results coincided almost exactly with those of Experiment 1, except that 
the simpler method, involving less jarring of the tubes, seemed to give the typhoid 
bacilli even a better chance of rising to the surface alone. 
Experiment 3. Isolation of B. typhosus from infected water 
As it was not possible to secure water which had been strongly suspected of 
contamination with typhoid faeces, 600 c.c. of tap-water were inoculated with two 
small loops of a young bouillon culture of B. typhosus^ and small amounts of this 
infected water were introduced into the sterile tubes as in Experiment 2. Five c.c. of 
20 per cent, gelatin were then introduced, mixed with the water, and finally 25 c.c. of 
12 per cent, gelatin containing bile-salt were added as before. The results are shown 
in Table 2. The cultures were made as before, from the surface of the fluid in the 
tubes, after incubation. 
TABLE 2 
Showing the result of an experiment to detect, by the use of gelatin tubes, 
typhoid bacilli in infected water : — 
Tube 
Amount inoculated at bottom 
of tube 
Plates made from surface of gelatin 
At start 
After 3 hours 
After zz hours 
A 
O'l C.C. 
Sterile 
Sterile 
Pure culture 
B. typhosus 
B 
CT2 C.C. 
do. 
do. 
do. 
C 
o - 5 c.c. 
do. 
Slight growth 
do. 
D 
I'O C.C. 
do. 
Sterile 
do. 
E 
2'0 C.C. 
do. 
Slight growth 
do. 
