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 



