120 CONTEMPORARY SCIENCE 



bacteria which are peculiar in that they do not migrate 

 throughout the body but remain fixed in a special tissue 

 or part, where they multiply and secrete a poison which 

 finds its way first into the lymph, then into the blood and 

 the organs generally. This latter class of microbes pro- 

 duces its effects to which we give the name of disease, 

 and of which diphtheria and tetanus are examples, through 

 the operation of a poison, peculiar to each, and in each 

 instance attacking by preference certain definite organs or 

 parts of them. Thus the poison elaborated by the diph- 

 theria bacillus selects especially the lymphatic organs, 

 heart and nervous system for its action, and the tetanic 

 poison the nerve cells governing muscular contraction. 



We have now returned by a route somewhat circuitous 

 perhaps to the point from which we started, namely diph- 

 theria and its antidote. But in the course of the journey 

 we have taken, new points of view have been gained 

 which, as will appear, are to transform entirely the out- 

 look upon the problems that bacteriologists set themselves 

 to solve. 



Behring and Kitasato chose the task of inducing in ani- 

 mals immunity, to diphtheria on the one hand and to 

 tetanus on the other. This was a logical undertaking and 

 one clearly in the spirit of the times. Both men had a 

 strong interest in the quest. The one (Behring) was 

 deeply engaged in the investigation of the chemical disin- 

 fectants and conceived ideas of modifying bacterial growth 

 through these agents, as Pasteur had succeeded in accom- 

 plishing with physical means. The other (Kitasato) had 

 succeeded where his predecessor and the discoverer of the 

 tetanus bacillus, Nicolaier, had failed in obtaining pure 

 cultures of that microbe. Moreover, the restricted local 

 development of the two bacilli and their generally poison- 

 ous or toxic effects aroused in them an eager interest in- 

 tensified by the epochal discovery just made by Roux and 

 Yersin that the toxin of the diphtheria bacillus was read- 

 ily separable from the bacilli producing it and could be 



