422 BACTERIOLOGY. 
move more slowly than before the addition of serum. 
Some of these soon cease all progressive movement, 
and it will be seen that they are gathering together in 
small groups of two or more, the individual bacilli 
being still somewhat separated from each other. Grad- 
ually they close up the spaces between them, and clumps 
are formed. According to the completeness of the 
reaction, either all of the bacilli may finally become 
clumped and immobilized or only a small portion of 
them, the rest remaining freely motile, and those 
clumped may appear to be struggling for freedom. 
With blood containing a large amount of agglutinating 
substances all the gradations in the intensity of the re- 
action may be observed, from those shown in a marked 
and immediate reaction to those appearing in a late and 
indefinite one, by simply varying the proportions of 
blood added to the culture fluid. 
Pseudo-reactions. If too concentrated a solution of 
‘dried blood from a healthy person is employed there 
will be an immobilization of the bacilli, but no true 
clumping. This is sometimes mistaken for a reaction. 
Again, dissolved blood always shows a varying amount 
of detritus, partly in the form of fibrinous clumps; and 
prolonged microscopical examination of the mixture of 
dissolved blood with a culture fluid shows that the 
bacilli, inhibited by substances in the blood, often be- 
come more or less entangled in these clumps, and in 
the course of one-half to one hour very few isolated 
motile bacteria are seen. The fibrinous clumps alone, 
especially if examined with a poor light by a beginner, 
may be easily mistaken for clumps of bacilli. Again, 
the bacilli may become clumped after remaining for 
one-half to two hours by slight drying of the drop or 
