INFECTION AND IMMUNITY. 479 



of animals several different bodies having totally differ- 

 ent relations to bacteria and their products, according to 

 the conditions under which they exist. First, there is 

 present in the blood-serum of practically all animals 

 the normal defensive ''alexines" already mentioned; 

 second, the antitoxins that are found in the blood of 

 animals artificially immunized from special sorts of 

 infection and intoxication, the functions of which are 

 susceptible of demonstration outside the body as well 

 as within the tissues of the living animal; third, a body 

 possessed of disintegrating bacteriolytic powers — i. e., 

 having the property of actually breaking bacteria to 

 pieces, so that the phenomenon may be observed under 

 the microscope. This jjhenomenon is especially to be 

 seen within the peritoneum of guinea-pigs that have 

 been rendered immune from Asiatic cholera and from 

 the typhoid and colon infections or intoxications. It is 

 rarely or never seen outside the body, and is not to be 

 confounded with the ordinary bactericidal function of the 

 alexiues that is demonstrable in most normal serums; 

 and fourth, a body,the so-called "agglutinin" (Gruber), 

 that is regarded by Widal to represent a "reaction of 

 infection," and not of immunity. The presence of 

 this body in a serum is announced by its peculiar influ- 

 ence on the activity and arrangement of bacteria with 

 which it is brought in contact. In the case of typhoid 

 fever in man, for instance, the serum obtained during 

 the early and middle stages of the disease, when mixed 

 with fluid cultures or suspensions of the typhoid bacil- 

 lus, causes the bacilli to lose their motility and to con- 

 gregate (agglutinate) together in masses and clumps, a 

 condition never seen in normal cultures of this organism, 

 and practically never observed when normal serum is 



