212 
HAROLD’S DISCUSSIONS. 
plant tissues as soon as death sets in. They are 
diminutive scavengers, and assist insects and worms 
in clearing the earth of dead bodies. Others seem 
Fig. 106.—Bacillus producing vinegar. 
to possess the ability to produce chemical effects and 
thus to change the nature of a substance, as the souring 
of milk and beer or flavoring butter and cheese. 
In their relation to man, bacteria may be classifled 
as the beneficent, those which assist him in producing 
advantageous results, and the malignant, whose work 
is injurious to him. 
We are just beginning to learn how to make the 
former serve us, and how to check the ravages of the 
latter. When we speak of bacteria, or germs, or 
bacilli, or microbes (the last is applied to any small 
life, animal or vegetable), we awaken prejudice at 
once. The truth is that the proportion of harmful 
species to the beneficent is no greater than that of 
poisonous plants to the useful ones. 
