amount of this soil is mixed thoroughly and the mixture solidified upon the walls of an Esmarch tube. The colonies are counted with the aid of a lens. Flügge found in virgin earth about 100,000 colonies in a cubic centi

meter.

Samples of earth, like samples of water, should be examined as soon as possible after being secured, for, as Günther points out, the number of bacteria changes because of the unusual environment, exposure to increased amounts of oxygen, etc.

The most important bacteria of the soil are those of tetanus and malignant edema, in addition to which, however, there are a great variety which are pathogenic for rabbits, guinea-pigs, and mice.

PART II. SPECIFIC DISEASES AND THEIR

BACTERIA.

A. THE PHLOGISTIC DISEASES.

I. THE ACUTE INFLAMMATORY DISEASES.

CHAPTER I.

SUPPURATION.

SUPPURATION was at one time supposed to be an inevitable outcome of the majority of wounds, and, although bacteria were observed in the discharges, the old habit of thought and insufficiency of information caused most surgeons to believe that they were spontaneously developed there.

Sir Joseph Lister, whose name we cannot sufficiently honor, conceived that Pasteur's observations upon the germs of life floating in the atmosphere, if they explained the contamination of his sterile infusions, might also explain the changes in wounds, and upon this idea based that most successful system of treatment known as "antiseptic surgery."

The further development of antiseptic surgery, and the extremes into which it was carried by alienists, almost attain to the ridiculous, for not only were the hands of the operator, his instruments, sponges, sutures, ligatures, and dressings kept constantly saturated with irritating germicidal solutions, but at one time the air over the wound was carefully saturated with pulverized antiseptic lotions during the whole operation by means of a steam atomizer. This rather monstrous outcome of the application of Lister's system to surgery was the very natural result of the erroneous idea that the germs which cause

the suppurative changes in wounds entered the exposed tissues principally from the atmosphere, and that the hands and instruments of the operator, while certainly means of infection, were secondary in importance to it.

The researches of more recent date, however, have shown not only that the atmosphere cannot be disinfected, but also that the air of ordinarily quiet rooms, while containing the spores of numerous saprophytic organisms, very rarely contains many pathogenic bacteria. We now also know that a direct stream of air, such as is generated by an atomizer, causes more bacteria to be conveyed into a wound than would ordinarily fall upon it, thereby increasing instead of lessening the danger of infection. It may therefore be stated, with a reasonable amount of certainty, that the atmosphere is rarely an important factor in the process of suppuration.

We have already called attention to the fact that various micro-organisms are so intimate in their relation to the skin that it is almost impossible to get rid of them, and have cited in this relation the experiments of Welch, Robb, and Ghriskey, whose method of disinfecting the hands has been recommended as the best. The investigations of these observers have shown that, no matter how rigid the disinfection of the patient's skin, the cleansing of the operator's hands, the sterilization of the instruments, and the precautions exercised, a certain number of wounds in which sutures are employed will always suppurate. The cause of the suppuration is a matter of vast importance in surgery and in surgical bacteriology, yet it is one which it is impossible to remove. We carry it constantly with us upon our skins.

Welch has described, under the name Staphylococcus epidermidis albus, a micrococcus which seems to be habitually present upon the skin, not only upon the surface, but also deep down in the Malpighian layer. He is of the opinion that it is the same organism which is familiar to us under the name of Staphylococcus pyogenes albus, but in an attenuated condition. If his opinion be correct,

and we have seated deeply in our derm a coccus which can at times cause abscess-formation, the conclusions of Robb and Ghriskey, that sutures of catgut when tightly drawn may be a cause of skin-abscesses by predisposing to the development of this organism, are certainly justifiable.

Not only does the coccus occur in the attenuated form described, but we have very commonly present upon the skin, generally as a harmless saprophyte, the important Staphylococcus pyogenes albus, which is a common cause of suppuration.

Although, as stated, the Staphylococcus pyogenes albus is a common cause of suppuration, it rarely occurs alone, the studies of Passet showing that in but 4 out of 33 cases which he investigated was this coccus found by itself. When pure cultures of the coccus are injected subcutaneously into rabbits and guinea-pigs, abscesses sometimes result; sometimes there is no result. Injected into the circulation of these animals, the staphylococci sometimes cause septicemia, and after death can be found

in the capillaries, especially of the kidneys. From these illustrations it will be seen that the organism is feebly pathogenic.

In the characteristics of its growth the Staphylococcus albus is almost identical with the species next to be described, but differs from it in that there is no golden color produced. Upon the culture-media it grows white. Generally present upon the skin, though in smaller numbers, is the dangerous and highly virulent Staphylococcus pyogenes aureus (Fig. 44), or "golden staphylococcus" of Rosenbach. As the morphology of this organism, and indeed the generality of its characters, are identical with those of the preceding species, it seems convenient to describe them together, pointing out such differences as occur step by step. In doing this, however, it must not be forgotten that, although the Staphylococcus albus has been described first, the Staphylococcus aureus is the more common organism of the suppurative diseases.

Although they had been seen earlier by several observers, the staphylococci were not isolated and carefully described until 1884, when Rosenbach worked upon them. The results of his study, followed by Passet and a host of others, have now given us pretty accurate information about them.

The cocci are distributed rather sparingly in nature, seeming not to find a purely saprophytic existence a suitable one. They occur, however, wherever man and animals have been, and can be found in the dust of houses, hospitals, and especially surgical wards where proper precautions are not exercised. They are common upon the skin, they live in the nose, mouth, eyes, and ears of man, they are nearly always beneath the fingernails, and they sometimes occur in the feces, especially in children.

The cocci are rather small, measuring about 0.7 μ in diameter. When examined in a delicately-stained condition the organisms may be seen to consist of hemispheres separated from each other by a narrow interval. The contiguous surfaces are flat, thus differing from the gonococcus, whose contiguous surfaces are concave.