154 
PRINCIPLES OF BACTERIOLOGY 
in each first tube put 0.2 c.c. of the patient’s serum, and 
continue the dilution along as described above, i. e., take 
1 c.c. from first tube to the second, from the second to the 
third, and so on, in each row; throw away the last c.c. 
(that is, from the 10th tube). Now to each tube in the 
“typhoid” row add 0.5 c.c. of typhoid culture with salt 
solution and killing it with 2 per cent of formalin, to each 
tube of the paratyphoid A row add 0.5 c.c. of the para¬ 
typhoid A culture, and so on. Incubate for one hour 
at 37.5° C. and examine. The row containing the tube 
with the highest dilution gives you the nature of the 
patient’s disease. 
Sometimes the so-called “microscopic Widal test” is 
made; this consists of making two or three dilutions 
(usually 1:20, 1:40, and 1:80) with patient’s serum, and 
a drop of each is mixed with a drop of typhoid emulsion, 
and placed on a cover-glass which is then placed over a 
“hanging drop” slide, as described elsewhere, after one 
hour the slide is examined to see if motility has ceased 
and clumping has taken place. This is a convenient quick 
test, but not nearly so comprehensive as the preceding 
method. 
VIII. Immune Treatment 
Whether the use of the typhoid vaccine is to be 
adopted for the treatment of typhoid fever is rather doubt¬ 
ful; but the use of such vaccine for the prevention of 
typhoid fever is not only an established fact but con¬ 
stitutes one of the most glorious achievements in bac¬ 
teriology and prevention of infectious diseases, and is 
one of the greatest medical services rendered the world 
by the English and American scientists. 
In England, the preventive use of vaccine was brought 
to perfection by Sir Wright, and in 1907-8, Major (now 
Colonel) Russell of the United States Army Medical 
