io8 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
accordingly centrifugalized in an electric centrifuge (two thousand revolutions per 
minute) for lengths of time varying from fifteen to sixty minutes. Plates were made 
from the surface in the method outlined by von Drigalski and Conradi, 1 and, 
although the number of bacilli was found to be less directly after the centrifugaliza- 
tion than just before, yet the difference was not striking. 
It was evidently desirable to deliver the suspected material at the bottom of a 
tube, if possible, and to liberate it there into a large quantity of medium in such a 
way as to prevent bacilli from rising to the surface at once, as they would if the 
inoculation were directly into bouillon. The technique of the first experiment was 
suggested during the reading of an article by Harris, 4 ' Concerning an Improved 
Method of making Collodium Sacs.' 
Experiment i. Gelatin capsules 
Into to c.c. of bouillon were inoculated one loop of a young bouillon culture 
of B. typhosus, and three loops of a similar culture of B. coli. Gelatin capsules 
containing 0*5 c.c. of the above mixture were deposited at the bottom of each of twelve 
sterile tubes, and over each capsule were poured 5 c.c. of 12 per cent, gelatin, and this 
was allowed to harden. The capsule was now completely imbedded in gelatin. After 
a few trials it was found desirable to place the tubes in the thermostat for fifteen 
minutes before allowing the gelatin to harden, in order to expel the air-bubble, which 
was of course present at the upper part of the gelatin capsule. Over the hardened 
gelatin there was poured, in six of the tubes, 15 c.c. of gelatin (12 per cent.), containing 
bile-salt (o - 5 per cent.), and in the other six 25 c.c. of the same fluid.* There 
was now present at the bottom of each tube a mixture of typhoid and colon bacilli 
imbedded in gelatin, and above it a column of sterile gelatin, all of which was sure to 
melt as soon as placed in the thermostat. It was hoped by this method to give the 
typhoid bacilli the best possible chance to get away from the colon bacilli. Plates were 
made from the surface of each tube, the gelatin was allowed to harden, and then all 
twelve tubes were placed in the thermostat at 37 0 C. At intervals of one hour, the 
gelatin being again in a liquid state at that temperature, one loop was taken from the 
surface of each tube, and stroked over the surface of plates of neutral-red lactose 
agar. 2 The results were very uniform, as shown in table 1. 
TABLE I 
Alter 1 hour 
After 2 hours 
After 3 hours 
Plates from surface of tubes containing 
20 c.c. gelatin ... 
Sterile 
Growth 
Growth 
Plates from tubes containing 
30 c.c. gelatin ... 
. do. 
Sterile 
do. 
* The use of bile-salt, as a means of inhibiting the growth of non-intestinal organisms, has already become familiar, 
in MacConkey'sS medium 'bile-salt agar.' 
