color to pus.

Nourishment and oxygen are carried to the tissues by the red blood corpuscles. Under circumstances which we shall see later, these are also altered both in number and in size, and also in their arrangement in the vessels. (See Chapter IV, “Inflammation.”)

THE LYMPHATIC SYSTEM

Waste material in the tissues is carried off by the return blood in the veins and also by the lymphatics. These are in reality the scavengers of the body, both the lymphatic vessels and glands, performing important functions for the good of the economy. They are found beneath the skin and in the subcutaneous tissue, also along the course of the great veins.

The lymphatics far exceed the veins in number and perform a function similar to the veins, gathering waste material from the tissues, also the digested food called chyle, from the stomach and intestines. The lymphatic vessels, also the lacteals which absorb the chyle, all pass through glands, which are extremely numerous, where certain deleterious substances are extracted from the lymph before it is emptied into the blood stream.

The lymphatic glands in performing their function as filters often become inflamed and when large numbers of pathogenic bacteria, or very virulent ones are contained in a gland, abscess formation results just as it would in any tissue so invaded.

CHAPTER II

SURGICAL BACTERIOLOGY

A microorganism or microbe, some species of which cause all disease, is a minute plant or animal too small, as a rule, to be visible to the naked eye.

The word germ may be used to designate any microorganism, but it has so many other meanings and has been so loosely employed even in this sense, that it cannot be used for accurate scientific description.

Bacteria are minute plants on the order of fungae, many of which are able to produce fermentation, decomposition or disease.

Although the word bacterium by derivation has the same meaning as bacillus and indicates a rod shaped fungus, it has been so loosely employed that it may very well be applied to the entire germal family, retaining the word bacillus in the narrower sense.

Description of Bacteria. Schizomycetes is the name given all the bacteria of putrefaction and disease, the former being called saprophytic and the latter pathogenic.

Bacteria are minute fungi, each consisting of a single cell enclosed in a cell membrane of cellulose which can be demonstrated by iodine, the latter causing the protoplasm to retract from the cell wall. There is no nucleus or central core. Some of the bacteria are colorless, others pigmented, yellow, blue or red. The cells vary in shape and in size in different species as well as in their mode of growth, and are named in accordance with these peculiarities. The round or oval cells are called cocci; the rod-shaped organisms are termed bacilli. The cocci are called micrococci or macrococci according to their size; diplococci or tetracocci, according to the production of pairs or groups of four in their multiplication; streptococci, because in their growth they always form chains of cells; staphylococci, because they grow in irregular clusters resembling bunches of grapes. Some of the bacteria have the power of motion generally produced by cilia or flagella and others are motionless.

Habitat. These organisms may truly be said to be omnipresent. Every thing we wear or use or eat, even the air itself, is impregnated with them. Pathogenic germs may also be found among these myriads. Every species has its own particular habitat, where the conditions especially favor its growth, just as any of the larger plants require a certain soil, a supply of water, temperature, and proper amount of light in order to make growth and multiplication possible.

The bacteria in the air are more numerous in dry weather, being carried up as dust by the wind, for a moist surface holds any bacteria which may lie upon it. So complete is the action of moisture, that air, which contained 600 microorganisms when inspired, has been shown to return from the lungs with almost none, the moist respiratory surfaces catching and holding the bacteria; so that the expired air is practically sterilized; this is true even when the expiration is from diseased lungs. The act of coughing, however, may expel bacteria in the mucus ejected. The number of bacteria in the air is very variable, but is much greater in houses than out of doors, and is naturally increased by attempts to clean the rooms.

Parasitic Nature. The number of species of pathogenic germs is comparatively small compared with the number of all the varieties of germs, for the latter are practically innumerable. Indeed, the wonderful qualities of resistance in animal tissues is the only thing that makes animal life possible and it is this power of resistance that allows certain wounds to heal by primary union when left without protection or care.

The schizomycetes are unable to extract nitrogen from the air or the soil, like the higher vegetables, and must, therefore, be provided with a higher nitrogenous compound, such as is produced by vegetable and animal life. Some of them are able to live upon dead organic matter, while others cannot exist without living tissues to feed upon and are therefore true parasites. There are some which are able to live upon either dead or living tissues and are known as facultative parasites, a class which includes a majority of pathogenic germs. Some organisms require albuminous matter, others need carbohydrates; they all require water, carbon, nitrogen, oxygen, and certain inorganic materials, especially lime and potassium. All organisms require water. If dried, no form will multiply, and many forms will die.

The fluids and tissues of the individual may or may not afford a favorable soil for the germs of a disease, or, in the same person afford it at one time, and not at another. Some individuals seem to possess indestructible immunity from, and others are especially prone to, certain contagious diseases. Impairment of health, by alterating some subtle condition of the soil, may make a person liable who previously was exempt.

Effect of Oxygen. Some bacteria need free oxygen; some can live either with or without free oxygen, while others cannot live at all in the presence of free oxygen. Those requiring oxygen are called aerobic; those which can live with or without it are called facultative aerobic; those which do not live in free oxygen are called anaerobic.

Bacteria are very sensitive to temperature, few being able to live in a temperature below 68°F. or 29°C. or above 104°F. or 40°C. The pathogenic varieties thrive best at about the normal temperature of the blood. Direct sunlight retards their growth and may kill them. Freezing renders bacteria motionless and incapable of multiplication, but it does not kill them; they again become active when the temperature is raised. The absurdity of employing cold as a germicide is evident when it is known that a temperature of 200°F. below zero is not fatal to germ life, cell activities by such a temperature only being rendered dormant. The high temperatures are fatal to bacteria, moist heat being more destructive than dry heat, and adult cells are more easily killed than spores. A temperature less than 212°F. will kill many organisms and boiling will kill every pathogenic organism that does not form spores. Some spores are not destroyed after prolonged boiling and some will withstand a