82 INFECTION AND RESISTANCE 



conditions and the difficulties of accurate measurements obtaining in 

 experiments upon in vitro bactericidal phenomena. For although a 

 specimen of the blood of a naturally immune animal may be capable 

 of destroying a considerable number of bacteria of a given species, the 

 implantation of such a specimen with a slight excess of the bacteria 

 would soon exhaust the active serum constituents and profuse growth 

 could then take place. Furthermore, the 'conditions of temperature 

 established in cultural experiments lead rapidly to a deterioration 

 of the alexin necessary for bactericidal action, and any bacteria 

 remaining alive at the end of a number of hours would then have un- 

 opposed opportunity to multiply. 



The attempts to establish parallelism between phagocytic activity 

 and natural immunity, though somewhat more successful than the 

 analogous efforts of the humoral school, nevertheless also failed to 

 furnish complete explanation for existing conditions, and, as we shall 

 see, no adequate generalizations could be made until later years re- 

 vealed the close cooperation between cells and fluids. We must post- 

 pone any attempts to do justice to this phase of the problem, there- 

 fore, until we are in a position to discuss the question of phagocytosis 

 on the basis of a fuller knowledge of the phenomena which influence 

 it 



The clear thinking and unprejudiced logic brought to bear upon 

 this controversy by some of the great bacteriologists of this time are 

 nowhere more instructively illustrated than in a short introduction 

 published by v. Behring 12 to his second article on diphtheria. He 

 says: "Neither deduction nor theorizing can at present decide 

 whether a compromise will be found in the future between the two 

 hypotheses (humoral and cellular), or whether the one or the other 

 alone will be found correct. As yet the opinions of many experiment- 

 ing bacteriologists are in direct opposition in this respect. Mean- 

 while, for the purposes of medical advancement and therapeutic suc- 

 cess it is not necessary to await a decision of this question. ... It is 

 indeed of advantage to the cause if the struggle against infection is 

 undertaken from the most varied points of view; attempts to make 

 proselytes for a dogma have never led to progress. In this sense I will 

 try to summarize those experimental results which support the hu- 

 moral point of view without attempting particularly to detract from 

 the importance of opinions which I do not share." 



THE PHENOMENA FOLLOWING UPON ACTIVE IMMUNIZATION 



The cellular and humoral points of view, formulated largely upon 

 the facts of natural immunity, were equally applied, almost from 

 the beginning, to the explanation of active immunization. The light 

 12 v. Behring. Zeitschr. /. Hyg., Vol. 12, 1892, 



