PREFACE. Vll 



false notions must be replaced by those which are 

 sounder and more j ust. 



For this reason, we have endeavoured to make 

 this work intelligible to all. It may be read with 

 profit by those who possess the elementary notions 

 of natural science which are included in the course 

 of primary instruction. We therefore hope that the 

 volume may find a place in the libraries of secondary 

 instruction, and in public libraries. 



Although the work is not specially intended for 

 physicians, yet practical men may not be indisposed 

 to glance at it : it may, at any rate, serve as an intro- 

 duction to the much more learned works of Cornil 

 and Babes, of Duclaux, Klein, Koch, Sternberg, etc. 

 We have given an important place to the botanical 

 question, which is too often neglected in works on 

 microbian pathology. From this point of view, the 

 narrow bond which connects bacteria with ferments 

 and moulds has to some extent marked out the plan 

 we have adopted ; namely, that of passing from the 

 known to the unknown, from what is visible with the 

 naked eye to that which is only visible with the aid 

 of the microscope. 



ANGERS, September 10, 1885. 



