SOME PROBLEMS IN THE LIFE-HISTORY OF 

 PATHOGENIC MICRO-ORGANISMS 



BY THEOBALD SMITH 



[Theobald Smith, Professor of Comparative Pathology, Harvard Medical School, 

 since 1896; Director of the Pathological Laboratory, Massachusetts State Board 

 of Health, b. Albany, New York, July 31, 1859. Ph.B. Cornell University, 1881 ; 

 M.D. Albany Medical College, 1883; A.M. (Hon.) Harvard. Assistant and Di- 

 rector of Pathological Laboratory, Bureau of Animal Industry, U. S. Depart- 

 ment of Agriculture, 1884-95; Lecturer and Professor of Bacteriology, Medical 

 Department, Columbian University, 1886-95; Member of the Board of Directors, 

 Rockefeller Institute for Medical Research, 1901-. Member of the American 

 Academy of Arts and Science; Association of American Physicians; Ameri- 

 can Public Health Association; Association of Pathologists and Bacteriologists. 

 Author of many papers and reports on infectious diseases of animals ; also papers 

 on bacteriology and general pathology.] 



OUR knowledge of the profound influence which the microscopic 

 organisms, known as the bacteria, exercise in the life of the globe, may 

 be considered an acquisition of the last quarter-century. The surmises 

 and hypotheses of the half-century preceding were then made over 

 into well-attested facts. 



The activities of micro-organisms manifest themselves in many 

 different ways. The functions carried on by the bacteria of the soil 

 are known to be of fundamental importance to higher plant life. The 

 work of the bacteria producing fermentation, putrefaction, and decay 

 is of similar importance in preparing the way for the soil bacteria and 

 ministering to the wants of higher organisms. Out of this latter class 

 there has arisen a group which has given these micro-organisms all the 

 notoriety they possess. It is a small group, but formidable in that it 

 is in partial opposition to the higher forms of vegetable and animal 

 life. It is these parasitic forms to which I shall devote my address, as 

 it is they which have preoccupied my attention for some years. In 

 thus passing over large groups of bacteria I simply register my inabil- 

 ity to properly present their claims, and I trust that others here 

 present will fully supplement my paper by dealing with them in 

 deserving fashion. 



While bacteriology, strictly speaking, deals only with a fairly well- 

 defined group of unicellular plant-like forms standing near the limit 

 of microscopic vision, medical bacteriology has been gradually widen- 

 ing its scope to a study of all unicellular and even higher parasitic 

 forms, which multiply more or less indefinitely and continuously for 

 a time in the invaded body. In addition to the bacteria proper, the 

 protozoa, and those highly important ultra-microscopic organisms 

 which seem to have certain characters not possessed by either of the 

 other two groups, are now frequently gathered into medical bacteri- 



