152 
PRINCIPLES OF BACTERIOLOGY 
gas bubbles will be seen (because the typhoid does not 
form gas on glucose) ; if the culture is paratyphoid, again 
only part of a tube will turn to red but gas bubbles will 
also be seen in the red part only (because the paratyphoid 
bacilli form both acid and gas on glucose and do not 
ferment lactose); finally if the culture should be con¬ 
taminated with colon bacillus, the culture tube will be 
red and gas bubbles will be seen everywhere (because 
the colon bacillus produces both acid and gas on both 
the glucose and the lactose). If this is insufficient ag¬ 
glutination should be done as follows: 
Four rows of Wassermann test tubes (4 x % inch) 
should be arranged, each row containing 10 test tubes; 
the first row is labeled “typhoid,” the second “para¬ 
typhoid A,” the third “paratyphoid B,” and the fourth 
“colon.” In the first tube of each row put 1.8 c.c. of 
sterile physiologic (0.8 per cent) salt solution, in all 
other tubes put 1 c.c. of salt solution; then into the first 
tube put 0.2 c.c. of the typhoid immune serum of known 
agglutinating properties (prepared by injecting the rab¬ 
bit three or four times with typhoid vaccine); now we 
have in this tube a 1:10 dilution of typhoid serum 
(1.8 c.c. salt solution and 0.2 c.c. of serum); take 
one c.c. out of this tube and put it into the 
next tube of the ‘‘typhoid” row; we had before 
in that second tube 1 c.c. of salt solution, now 
we have 2 c.c. of fluid, one c.c. being salt solution, 
the other c.c. being 1:10 dilution of the immune typhoid 
serum from the first tube, so that the second tube con¬ 
tains the serum in dilution 1:20; repeat this process until 
the last tube is reached, and throw away the last c.c.; 
all tubes now contain 1 c.c. of fluid, but the dilutions 
are all doubled, the amount of serum being halved as 
we go from one tube to another: 1st tube, 1:10; 2nd, 
