TYPHOID BACILLUS 375 
practice the film of dried blood is diluted with physiological normal 
saline solution to a pale rose color, which corresponds to a dilution of 
1 to 20. An equal volume of typhoid bacilli (broth culture) is added, 
and the results determined in the usual manner. This dilution is 
somewhat inaccurate and anemic bloods introduce a disturbing]: factor. 
This method of dilution, however, is sufficiently accurate for all except 
unusual cases, and it is a method generally used in routine board of 
health examinations. Downs, ^ however, has shown that agglutinations 
made with dried blood are weaker, and less satisfactory than those 
made with fresh serum drawn from the clot of the same blood sample. 
(6) Blood Senim.—A few drops of blood are collected in a capillary 
pipette or small test-tube and allowed to clot. The serum is removed 
and diluted accurately with salt solution. The advantages are: (1) 
The accuracy with which dilution may be made; and (2) the ease 
with which serum is obtained. The disadvantages are: (1) That 
blood serum is readily contaminated; and (2) it does not keep well, 
it deteriorates. Blood serum is the best for accurate work. 
(c) Blister Fluid.— This possesses no advantages over blood serum. 
It is somewhat more difficult to obtain and probably somewhat less 
accurate than blood serum. 
(d) Uliole Blood.— Aside from clotting, whole blood is as reliable 
as blood serum, so far as accuracy of dilution and potency of agglu- 
tinins is concerned. It must be remembered, however, that the red 
blood cells appear in the field viewed under the microscope. Fresh 
whole blood presents one great disadvantage— the fibrin in it may 
cause a pseudo-agglutination, for the fibrin network that forms as 
coagulation proceeds entangles typhoid bacilli in its meshes, giving 
the appearance of a true agglutination. Whole blood can be con- 
veniently drawn into a blood-counting pipette and diluted accurately 
and immediately. 
The Culture to he Vsed.—0\d stock cultures of typhoid bacilli usu- 
ally give the best results. Freshly isolated cultures not infrequently 
agglutinate less readily than those which have been on artificial media 
for some time. The organisms should be grown in 0.1 per cent, 
glucose broth for eighteen hours at 30° to 32° C. It has been found 
that typhoid bacilli grown at this temperature agglutinate somewhat 
better than those grown at 37° C. Killed cultures are frequently 
used, but the results obtained are somewhat less accurate than those 
with living cultures. In rare instances it has been found that killed 
cultures will agglutinate with typhoid sera at 45° C. when living 
cultures fail to agglutinate. Dreyer, however, has used formalized 
cultures, which have been carefully standardized both with reference to 
relative agglutinability (reduction factor), and density, for purposes of 
quantitation of the agglutinins in serum, with much success. Such 
standardized cultures are valuable especially for measuring changes 
1 Univ. Kansas Sci. Bull., 1926, 16, No. 1. 
2 Jour. Pathol, and Bacteriol., 1909, 13, 331. 
