BACILLUS COLI COMMUNIS 



397 



specificity of the agglutination reaction. Thus a serum which will 

 agglutinate its homologous strains in dilutions of one 1 : 1,000 will often 

 fail to agglutinate other races of Bacillus coli in dilutions of 1-500 

 or 1 : 600. 



The normal serum of adult animals and man will often agglutinate 

 this bacillus in dilutions as high as 1 : 10 or 1 : 20 a phenomenon pos- 

 sibly referable to its habitual presence within the body. Corrobo- 

 rating this assumption is the observation of Kraus and Low, 1 

 that the serum of new-born animals possesses no such agglutinating 

 powers. The fact that agglutinins for the colon bacillus are increased 



12 3 



FIG. 85. BACILLUS COLI COMMTTNIOR. Grown in: 1. Dextrose, 2. Lactose, 3. 



Saccharose broth. 



in the serum of patients convalescing from typhoid fever or dysentery 

 is probably to be explained, partly by the increase of the group agglu- 

 tinins produced by the specific infecting agent, and partly by the in- 

 vasion of colon bacilli, or the absorption of its products induced by the 

 diseased state of the intestinal mucous membrane. 



Varieties of the Colon Bacillus. During the earlier days of bacterio- 

 logical investigations, a large number of distinct varieties of colon bacilli 

 were described, many of which may now be dismissed as based simply 



1 Kraus und Low, Wien. klin. Woch., 1899. 



