424 BACTERIOLOGY. 
Advantages and Disadvantage of Serum and. Dried 
Blood for the Serum Test. The dried blood is easily 
and quickly obtained, and does not deteriorate or be- 
come contaminated by bacterial growth. It is readily 
transported, and seems to be of nearly equal strength 
with the serum in its agglutinating properties. It 
must in use, however, be diluted with at least five 
times its bulk of water, otherwise it is too viscid to be 
properly employed. The amount of dilution can only 
be determined roughly by the color of the resulting 
mixture, for it is impossible to estimate accurately the 
amount of dried blood from the size of the drop, and 
it is too much trouble to weigh it accurately. Serum, 
on the other hand, can be used in any dilution desired, 
varying from a mixture which contains equal parts of 
serum and broth culture to that containing 1 part of 
serum to 100 parts of culture, and this can be exactly 
measured by a graduated pipette, or, roughly, by a 
_ measured platinum loop. The disadvantages in the 
use of serum are entirely due to the slight difficulty in 
collecting and transporting it and the delay in obtain- 
ing it when a blister is employed. If the serum is 
obtained from blood after clotting has occurred a 
greater quantity of blood must be drawn than is neces- 
sary when the dried-blood method is used; if it is 
obtained from a blister, a delay of six to eighteen 
hours is required. The transportation of the serum 
in capillary tubes presents no difficulties if tubes of 
sufficiently thick and tough glass are employed and 
placed in tiny wooden boxes. For scientific investiga- 
tions and for accurate results, particularly in obscure 
cases, the use of fluid serum is to be preferred to dried 
blood. Practically, however, the results are nearly as 
