CAUSES OF DISEASE. 27 
from without; taken up into the body, it can call a specific disease into action, 
but it cannot spread that malady any farther by conveying it from a diseased to 
a sound dog. 
Disease-producing poisons are termed volatile and fixed. 
The so-called germ theory of disease now explains the causation of some 
of the infectious diseases, and without doubt additions to the number will be 
constant, although necessarily slow. To discuss that theory comprehensively 
herein would not be possible, far too much space being required; it will there- 
fore be touched on only very lightly. 
The organisms which produce disease are called bacteria. This name, which 
properly belongs to a peculiar species and has been generalized, covers the 
smallest and at the same time simplest and lowest, of all living forms. They 
either constitute the boundary line of life or are indeed very near it. Notwith- 
standing the colossal amplification of microscopes of the present, the smallest 
bacteria do not appear larger than the points and commas of good print; and 
the smallest has not inaptly been compared with man about as a grain of sand 
to Mont Blanc. The part played by bacteria in nature is an important one. 
They exist everywhere, and have their use in the general economy. They are 
nourished at the expense of organic substances when in a state of putrefaction, 
and reduce the complex constituents of the same into those which are simpler, 
—into the soluble mineral substances which return to the soil from which the 
plants are derived, and thus serve afresh for the nourishment of similar plants. 
In this way they clear the surface of the earth from dead bodies and filth, from 
all the dead and useless substances which are the refuse of life, and so unite 
animals and plants in an endless chain. But besides these useful bacteria or 
microbes there are others which are injurious to mankind and the lower orders 
of animals, while they fulfil the physiological destiny marked out for them by 
nature. Such are the microbes which produce most of the changes in food and 
industrial substances, and a large number of the diseases to which man and 
domestic animals are subject. The germs of these diseases, which are only the 
spores or seeds of the microbes, float in the air breathed and in the drinking- 
water, and thus penetrate to the interior of bodies. 
Certain causes of disease are distinguished as traumatic, and the affections 
produced by them are termed traumatic diseases. Anything which occasions an 
injury or wound of a part, and consequently disease of that part, is a traumatic 
cause. 
Puppies are seldom born with transmitted diseases, but where either of the 
parents is the victim of disease or constitutional infirmities, the offspring very 
generally exhibit strong tendencies to those same or other defects; and such 
generally appear in them about the time of life that their parents first suffered, 
unless their coming is hastened by improper feeding or other faults in man- 
agement. 
