PROBLEMS OF PATHOGENIC MICRO-ORGANISMS 221 



rather unique state of affairs, bacteriology is not a self-contained, 

 well-defined field of work, but one greatly subdivided by aims and 

 methods of study. A realm as large as that of micro-organisms may wel 1 

 claim attention in many workshops of science. 



The short time at my disposal does not permit a wide survey of the 

 field of bacteriology, and I have deemed it best to discuss in a general 

 way the parasitism of bacteria and to outline the probable results of 

 any attempts of medical and sanitary science to modify this parasit- 

 ism. In undertaking this task 1 have adopted the somewhat discred- 

 ited method of presenting actual hypotheses, partly new, partly old, 

 in a new dress. These furnish a definite point of attack, and are better 

 suited for discussion than any presentation which boxed the compass 

 with the views already well known. 



Infectious diseases have frequently been portrayed as a battle 

 between two organisms, the host on the one hand, the parasite on 

 the other. There are few diseases, even among those not strictly in- 

 fectious in character, in which this battle does not go on at some stage, 

 and in which the activity of bacteria may be ignored. For some years 

 the analysis of this warfare has been the chief problem of bacteriology 

 and pathology. What are the weapons of offense and defense on 

 either side? Are the weapons simple or complex? Are they changed 

 as the struggle progresses to suit the immediate state of the battle? 

 Do the combatants themselves change during long or short periods 

 of time, and does the character of the disease change as a consequence? 

 Is the behavior of parasites, when posing for us in the culture-tube, 

 different from that in the animal body? These and other queries 

 may easily be read into the special literature of the last decade. 



To realize the great complexity of this struggle we need but to review 

 the gross facts of disease which express themselves in epidemics, on the 

 one hand, in individual disease, on the other. We meet all gradations 

 of severity, from rapid death to a mild transient disturbance, from a 

 disease lasting hours to one lasting fifteen or twenty years, or even 

 longer. Even the simplest generalizations concerning such a varied 

 phenomenon must necessarily be subject to many exceptions, and 

 perhaps gross inaccuracies. This is evident from the heated discus- 

 sions which have been waged over the humoral and cellular phe- 

 nomena, the antitoxic and bactericidal forces of the blood, and the 

 phagocytic activities of certain cells, each party to the discussion 

 claiming, at least for a time, that the opponent had no case. Though 

 the brilliant researches of Metchnikoff and Ehrlich, and the funda- 

 mental discovery of Behring and Kitasato, have to a certain degree 

 exposed the mechanism of warfare, the exposure is only fragmentary, 

 and the hypothetic reconstructions based on it are leading as usual 

 to further controversy. We do know that no two species of micro- 

 organisms carry on the warfare just alike, and that the same parasite 



