480 BACTERIOLOGY. 



employed. There are evidences of the presence of 

 "agglutinin" in certain of the antitoxic serums from 

 immune animals, viz., that of animals immune from 

 cholera, pyocyaneus, typhoid and colon infections. So 

 far as experience has gone, this agglutinating influence 

 is manifested in the great majority of cases only upon 

 the organisms from which the animal is protected. In 

 view of the fact that its presence is regarded as indica- 

 tive of a reaction of infection, its detection in the blood 

 of immune animals may at first sight appear paradoxi- 

 cal. We should not lose sight of the fact, however, 

 that it is assumed to be totally distinct from the other 

 substances that are concerned in immunity, and its pres- 

 ence in immune animals may, therefore, be reasonably 

 explained as a result of the " reactions of infection" 

 that were coincident with the primary injections into 

 the animal of infective or intoxicating matters neces- 

 sary to the establishment of the condition of immunity. 

 The experiments that have been cited afford but an 

 imperfect idea of the enormous amount of work that 

 has been done upon the manifold phases of these im- 

 portant subjects; they may, however, serve to indicate 

 the direction in which the lines of research have been 

 laid. As a result of such investigations, our knowledge 

 upon infection and immunity may at present be sum- 

 marized about as follows : 



1. That infection may be considered as a contest be- 

 tween bacteria and living tissues, conducted on the part 

 of the former by means of the poisonous products of 

 their growth, and resisted by the latter through the 

 agency of proteid bodies normally present in and gen- 

 erated by their integral cells. 



2. That when infection occurs it may be explained 



