vi PREFACE. 
of the beings in question, or could give an exact 
account of the function which microbes fulfil in 
nature.. And yet this function concerns us all. 
The man of the world who desires to take part in 
a scientific discussion; the lawyer who has to treat of 
a question of hygiene in the presence of experts; the 
engineer, the architect, the manufacturer, the agricul- 
turist, the administrator—all have to consider such 
questions, and they will find in this work clear and 
precise notions on microbes, notions which they would 
find it difficult to glean from books designed for 
physicians and professional botanists, 
The questions of practical hygiene, those which 
concern domestic economy, agriculture, and manufac- 
tures, and which are connected with the study of 
microbes, must especially demand attention. These 
are pertinent questions in such a book as this. There 
is a certain danger in vulgarizing notions of medicine, 
strictly so called; but it can only be beneficial to 
make every one acquainted with the precepts of hy- 
giene, which cannot become popular until they have 
penetrated into the habits and routine of national 
life. 
There is much to be done before modern society 
is practically on a level with the achievements of 
science; many prejudices must be uprooted, and many 
