Tue Microscope. 255 
this or something similar in Plymouth, Pa., are well remembered. 
In my own town, of ten thousand inhabitants, a small, open 
stream of water, almost failing in mid summer, receives the sewage 
and filth, inevitably collected in its course through the suburbs of 
the place. Cows are permitted to run at large upon the wide open 
commons and to drink at will from this polluted water. No evi- 
dence is now needed that milk from cows drinking the water car- 
rying the germs of typhoid fever, may communicate the disease, 
This is an incontestable fact. Sometime, I fear, when it is too late, 
our people will recognize the awful danger that attends a risk of the 
kind now pointed out; and yet our state board of health rates the 
town among the best in its sanitary condition. 
Third. How do bacteria cause disease? In all this talk about 
bacteria as disease agents, we are apt to think of them as specially 
distinct and different from all other living things, perhaps as en- 
dowed with some venomous properties like poisonous snakes among 
animals. But the fact is, these microscopic organisms are simple 
plants, living and dying, growing and multiplying, under condi- 
tions as circumscribed and laws as immutable as those which limit 
and govern other vitalized beings or things. They are far removed 
from anything that can be called malicious. They heed not the 
ruin wrought, but obeying the impressed law of vegetative growth 
simply, and only appropriate suitable food when and where it is 
supplied to them. Having no means of locomotion except on a 
microscopic scale, and this only in the case of certain species, they 
are subject, as to distribution, to the natural forces of air and water 
currents, gravitation, or the movements of other living things. 
They are destroyed by heat, in their vegetative condition never sur- 
viving that of boiling water continued some minutes, (as spores, re- 
sisting somewhat higher temperatures for longer periods,) poisoned 
by various chemical substances, and die at length from exposure 
and starvation. The bodies of living plants, animals and men are 
by nature carefully protected against these unarmed foes, by an 
epidermis or skin, usually impenetrable by them; by specially and 
wonderfully constructed guards, to prevent their entrance to vul- 
nerable openings, as the hairs moistened with mucus in the 
human nose, the moistened, vibrating cilia of the epithelial cells 
lining the road to the lungs. They are checked or entirely over- 
come by the natural secretions, like the etherial oils in plants (per- 
