INFECTION AND IMMUNITY. 573 



only on the elaboration of antitoxins, but also upon a 

 power on the part of the animal fluids to cause a com- 

 plete metamorphosis or disappearance of such participate 

 matters as bacterial and other irritating or poisonous 

 cells and substances. They believe the forces at work 

 in the establishment of immunity from bacteria and 

 from bacterial and other toxins, those operative in the 

 elaboration of the newly discovered lysins, antilysins, 

 agglutinins, precipitins, ferments, antiferments, etc., as 

 well as those concerned in physiological assimilation and 

 nutrition, to be fundamentally identical. They believe 

 susceptibility to infection, as well as power to assimilate 

 nutrition, to be explainable through the assumption that 

 special molecular groups of the living protoplasm are 

 endowed with specific combining affinities for particular 

 matters ; and in so far as the establishment of disease is 

 concerned, they regard the receptivity of the individual 

 to be determined entirely by the greater or less suscepti- 

 bility of those protoplasmic molecular groups " recept- 

 tors," as they designate them to disease-producing 

 agents. In individuals that have been artificially im- 

 munized from hurtful substances, they believe (in reit- 

 eration of Ehrlich's view expressed above) that the 

 receptive molecules have been more or less multiplied, 

 according to the degree of immunity, through bioplastic 

 activity of similar, unimpaired atom-groups surrounding 

 those more directly influenced by the intoxicant during 

 the process of immunization ; and that this excess of 

 such " receptors," although physiologically useless, being 

 of no known service to normal function, circulates un- 

 changed in the blood, and serves, through specific com- 

 bining affinity for the poison against which the animal 



