266 BACTERIOLOGY 



tinated" by the serum; the reaction being referable to the 

 presence of a new body "agglutinin" that has appeared 

 in the blood as a result of the infection or the vaccination. 

 The relation of this newly formed antibody is specific, i. e., 

 it agglutinates only those agents that called it forth. In 

 the normal blood agglutinating activity may often be de- 

 monstrated for a variety of bacteria (Bergey) but it is never 

 as high in potency as is that which may be artificially induced, 

 or that seen early in convalescence from a number of infec- 

 tions. 



The agglutinating properties of an immune serum are not 

 indicative of the degree of immunity possessed by the indi- 

 vidual from whom the blood was drawn. There may be a 

 relatively high degree of agglutinating property with no 

 demonstrable correspondence in germicidal or protective 

 activity. Though no parallelism necessarily exists between 

 the degree of agglutinating and that of germicidal or bac- 

 teriolytic activities of an immune serum, it is nevertheless 

 true that both qualities develop as a result of an effort on 

 the part of the tissues to resist infection, and both may 

 represent a response to the same stimulus. 



The specificity of the agglutinating reaction has proved 

 of use in the identification of infective bacteria, and con- 

 versely, in the recognization of diseases resulting from 

 bacterial invasion. For instance: given an unidentified 

 bacterium of the colon typhoid dysentery group that 

 is agglutinated by the serum from a case either of experi- 

 mentally induced or naturally acquired typhoid fever and 

 is not agglutinated by serum from a dysentery case or one 

 of colon infection in all human probability that organism 

 is the typhoid bacillus; or given the serum from a patient 

 suffering from an. undetermined febrile disease that agglu- 



