It was long ago noted by the chroniclers that the death-rate from wound-fever among the soldiers of a defeated army was apt to be much greater than among those of the victorious one, and this was quoted as one of the stock evidences of the influence of mind over body. But we now know that armies are not beaten without some physical cause, that the defeated soldiers are apt to be in poorer physical condition to begin with; that they have often been cut off from their base of supplies, have made desperate forced marches without food or shelter in the course of their retreat; and, until within comparatively recent years, were never half so well treated or well fed as their captors.
As the invading germs pass into the body, they travel most commonly through the lymph-channels and skin; are arrested and threatened with destruction by the so-called lymphatic glands, or lymph-nodes. This is why, if you have a festering wound or boil on your hand or wrist, the "kernels" or lymph-nodes up in your armpit will swell and become painful. If the lymph-nodes can conquer the germs and eat them up, the swelling goes down and the pain disappears. But if the germs, on the other hand, succeed in poisoning and killing the cells of the body, these latter melt down and turn to pus, and we get what we call a "secondary abscess."
The next commonest point of attack of these pus-germs, if they once get into the body, and by far the most dangerous, is the heart, as in rheumatism and other fevers. Some will also attack the kidneys, giving rise to albumin in the urine, while others attack the membranes of the joints (_synovia_) and cause suppuration of one or more joints in the body, which is very apt to be followed by very serious stiffening or crippling. So that, common, and, in many instances, comparatively mild as they are, the pus-germs in the aggregate are responsible for a very large amount of damage to the human body.
This is the way the _streptococcus_ and _staphylococcus_ behave in an open wound, or sore; but they have two other methods of operating which are somewhat special and peculiar. One of these is where the germ digs and burrows, as it were, underground, in a limited space, resulting in that charming product known as a boil, or a carbuncle. The other, where it spreads rapidly over the surface just under the skin, after the fashion of the prairie fire, producing _erysipelas_. In the first of these he behaves like the famous burrowing owl of our Western plains, who forms, with the prairie-dog, the so-called "happy family." He never makes his own burrow, he simply uses one which is already provided for him by nature, and that is the little close-fitting pouch surrounding the root of a hair. Whether the criminal is a harmless native white coccus which has suddenly developed anti-social tendencies, or a Mongolian immigrant who has been accidentally introduced, is still an open question. The probabilities are that it is more frequently the latter, as, while boils are absolutely no respecters, either of persons or places, and may rear their horrid heads in every possible region of the human form divine, yet they display a very decided tendency to appear most frequently in regions like the back of the neck, the wrist, the hips, and the nose. One thing that these areas have in common is that they are liable to a considerable amount of chafing and scratching as by collars and stocks on the neck, and cuffs on the wrists, or of friction from belts, or pressure or chafing from chairs or saddles. When the tissues have been bruised or chafed after such fashion, especially if the surface of the skin has been at the same time broken, and any pus-organism is either present in the hair-follicle, like the white coccus, or rubbed into it by a finger or finger-nail which has just been sucked in the mouth, used to pick the nose, or possibly engaged in dressing some wound, or cutting meat, or handling fertilizer, then all the materials for an explosion are at hand.