342 TYPHOID FEVER 



normally in a serum or they may be originated by an animal 

 being infected with a particular bacterium. As the result of 

 injecting a bacterium not only may agglutinins capable of 

 acting on that bacterium appear in the serum, but the serum may 

 become capable of agglutinating other, and especially kindred, 

 bacteria ; further, any normal agglutinins for the infecting 

 bacterium present in the serum may be increased in amount. 

 The agglutinin acting on the infecting organism has been called 

 the primary or homologous agglutinin, while the others have been 

 called the secondary or heterologous agglutinins. But besides 

 what we know to be a fact, that infection by a single bacillary 

 species can originate agglutinins acting both on itself and on allied 

 species, we must consider the possibility of infections by more 

 than one species occurring in an animal, e.g. b. typhosus with b. 

 coli or with b. paratyphosus. In such a case each organism 

 may originate its primary agglutinin so that the presence of 

 multiple agglutinins in a serum may really be an indication of 

 a mixed infection. Some attention has been directed to the 

 diagnosis and differentiation of these conditions. Castellani 

 has introduced a method for their investigation. This depends 

 on the capacity manifested by bacteria of absorbing the ag- 

 glutinins from a serum. A small quantity of the agglutinating 

 serum, say '5 c.c., is taken either pure or diluted with bouillon, 

 there are added 4 to 8 loops of an agar culture of the germ which 

 originated it, the mixture is well shaken and set at 37 C. for 12 

 hours. Clumping of course occurs, and the clumps fall to the 

 bottom of the tube. The supernatant fluid is pipetted off and 

 is available for further tests. Castellani studied the primary and 

 secondary agglutinins produced in infections in rabbits ; he found 

 that when an animal had been infected with b. typhosus this 

 organism would absorb from its serum not only the primary 

 typhoid agglutinins but also such secondary agglutinins as those 

 acting on the b. coli. If, however, an animal had undergone 

 infection with, say, both the b. typhosus and the b. coli, then the 

 b. typhosus could not absorb from its serum the b. coli (primary) 

 agglutinin. Castellani thus put forward the view that by this 

 means primary could be differentiated from secondary agglutinins, 

 and therefore pure could be differentiated from mixed infections. 

 There is little doubt that this view possesses considerable validity, 

 though it is probably not of universal applicability. Safe 

 deductions can only be drawn when any serum is tested with 

 several species of fairly closely related organisms, such as those 

 of the coli group. Especially is it necessary that the highest 

 dilutions in which agglutination occurs should be compared. If 



