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 



