VI PREFACE. 



essay in order that our knowledge of the causes 

 of putrefaction, fermentation and disease, to- 

 gether with the methods of the prevention and 

 cure of infection, may develop in a way free 

 from all ontology. It is sometimes of use 

 to restate things which are axiomatic. The 

 " entities " or u essences," which even in the 

 age which has discovered the law of the con- 

 servation of energy and the evolution of living 

 things by means of the struggle for existence, 

 still haunt the mind of the physician who re- 

 mains sunk in the ontological contemplation of 

 diseased cells and disease-producing bacteria, 

 are a mere remnant of priest medicine and can 

 have no place in any scientific conception of 

 biology, pathology or hygiene. 



Without trenching in any way upon the field 

 of works which aim at bringing together all 

 the material at our disposal or at the special 

 introduction of physicians to the subject, I may 

 be permitted to hope that this first mechanical 

 and monistic exposition of bacteriology will 

 be welcomed by many readers as a comple- 

 ment of the other works, and that it will com- 

 mend itself as a trustworthy guide to all who 

 wish to make themselves acquainted with the 

 present standpoint and the prospective pro- 

 gress of scientific bacteriology. For this rea- 

 son I have given adequate recognition not only 



