610 BACTERIOLOGY. 



on the part of the body to resist infection. The pres- 

 ence of this body in a serum of an animal is announced 

 by its peculiar influence on the activity and arrangement 

 of the particular species of bacteria from which the indi- 

 vidual is immune, or with which it is infected. In the 

 case of typhoid fever in man, for instance, the serum 

 obtained during the early and middle stages of the dis- 

 ease, when mixed with fluid cultures or suspensions of 

 the typhoid bacillus, causes the bacilli to lose their 

 motility and to congregate (agglutinate) in masses and 

 clumps, a condition never seen in normal cultures of this 

 organism, and practically never observed when normal 

 serum is employed. There are evidences of the pres- 

 ence of " agglutinin " in certain of the antitoxic serums 

 from artificially immunized animals, viz., that of ani- 

 mals immune from cholera, pyocyaneus, typhoid, dysen- 

 tery, and colon infections. So far as experience has 

 gone, this agglutinating property is manifested in the 

 great majority of cases only upon the particular organ- 

 isms from which the animal supplying the serum is 

 protected ; that is to say, the relation is specific. In 

 view of the fact that the power of a serum to agglutinate 

 bacteria is regarded by many as a concomitant of infec- 

 tion, the exhibition of this property by the blood of 

 immune animals may at first sight appear paradoxical. 

 We should not lose sight of the fact, however, that 

 agglutinin is presumably distinct from the other sub- 

 stances concerned in immunity, and its presence in im- 

 mune animals may, therefore, be reasonably explained 

 as a more or less permanent result of the " reactions of 

 infection" that were coincident with the primary stimu- 

 lations by specific infective or intoxicating matters nec- 

 essary to the establishment of the condition of immunity; 



