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 vaccinatibn. 

 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- 



