PREFACE. 



organisms, and I have adduced facts and arguments in 

 this work which I think justify the inference that 

 neither " microzymes," nor " bacteria," nor " fungi," 

 nor any of the lower forms of life are concerned in the 

 production or in the propagation of the contagious 

 fevers of animals and man. 



It seems to me probable that the subtle poison 

 originated and multiplied in man's own body, or in 

 the bodies of some of the animals domesticated by 

 man. I consider that it has been derived by un- 

 interrupted descent from the bioplasm or living matter 

 of an organism which at an antecedent period may 

 have been perfectly healthy. 



Man therefore can alone be held responsible for the 

 development of these disastrously potent particles ; 

 and I believe that if our predecessors had been accu- 

 rately acquainted with all the circumstances favourable 

 to the production and propagation of disease germs, 

 and had submitted to be guided by the laws of health 

 that might have been deduced from such knowledge, 

 we should now be living, even under the adverse con- 

 ditions imposed upon us by modern civilization, 

 without the risk of being decimated by pestilent 

 scourges. Such happiness, however, cannot be the 



