122 CONTEMPORARY SCIENCE 



of the inoculated material, in the hope that a mild and 

 not fatal infection would be induced from which recov- 

 ery would follow leaving the treated animal immune. 



The experiments were sometimes successful, and as 

 such seem merely to illustrate a variation of the Pasteur- 

 ian method of inducing immunity which, as we saw, was 

 not distinct in principle from the Jennerian vaccination. 

 But the break with the past was none the less imminent, 

 for Behring's next act was not to speculate on the theory 

 of immunity but to -per form a decisive experiment. It is 

 to be kept in mind that in the poisons or toxalbumins of 

 diphtheria and tetanus, we possess the essentially active 

 ingredients of the respective bacilli and that the body at- 

 tacked does not succumb to the invading bacilli but to the 

 action of the toxins. Hence, Behring turned to the blood 

 of the immune animals and tested it for neutralizing power 

 against the poisons, and 'discovered antitoxin ; he injected 

 the blood of an immune into the body of a normal animal 

 prior to inoculation and discovered passive immunization ; 

 and finally, he injected the blood of an immune animal 

 into animals previously inoculated with the bacilli of diph- 

 theria and tetanus, and discovered serum therapy. The 

 day for speculation on what constituted the immune state 

 had now definitely passed, and the time had arrived for 

 subjecting the phenomenon to experimental study. 



The fluids or "humors" of the body, to employ a term 

 made respectable by age, as represented by the serum of 

 the blood, had been shown to carry the immunity prin- 

 ciples, but what part did the cells of the body play in the 

 process ? Both fluids 'and cells were now submitted to 

 rigid and ingenious scrutiny, and about them an immense 

 literature has grown up. Soon the students in the field 

 divided into two camps, namely, one led by Ehrlich, de- 

 fending the humoral doctrine, the other led by Metchni- 

 koff, urging the cellular or phagocytic doctrine. The con- 

 flicts which raged about these concepts were always ani- 

 mated and sometimes even bitter ; but the ultimate effect 



