For twenty-one years I was able to study the reaction
of well-fed animals to epidemic diseases, such as
rinderpest, foot-and-mouth disease, septicemia and so forth,
which frequently devastated the countryside. None of my animals
were segregated, none were inoculated; they frequently
came in contact with diseased stock. No case of infectious disease
occurred. The reward of well-nourished protoplasm was a very high
degree of disease resistance, which might even be described as immunity.
Sir Albert Howard

The immune system is the name given to the complex organisation of glands, white cells, antibodies and other protein substances, hormones, enzymes and bacteria which protect the body against potentially harmful germs, viruses and foreign substances that may gain access to it. Foreign substances may include improperly digested protein molecules or other toxic matter from the digestive system as well as medicine and antibiotics also toxic to the body. The moment any of these substances enter the bloodstream they excite antagonism from the immune system and are therefore called antigens. Among the everyday activities of the white cells is the destruction and elimination of wornout red blood cells, which are continually replaced by the millions every second, and the elimination of any other cellular or metabolic debris.

White cells are called leucocytes and there are many types, each with a different way of working but co-operating together as circumstances require to achieve their joint purpose. White cells are constantly being manufactured in the bone marrow of the body and migrate to inhabit all the tissues and body fluids in great numbers, whereas red blood cells (erythrocytes) never leave the blood circulation.

Phagocytes are white cells which destroy antigens by consuming and digesting them. Macrophages are large phagocytes which can consume larger antigens such as defective or worn-out body cells. Neutrophils are the most numerous of the mobile phagocytes and are primarily concerned in attending to foreign germs or viruses. Lymphocytes are another type of white cell which patrol in the blood and lymph, there being two kinds: B lymphocytes, which manufacture antibodies, and T lymphocytes, which have other specialized functions for which they have been prepared in the thymus gland. Antibodies are specialised protein substances which B lymphocytes produce in large numbers when necessary to help destroy an antigen of a particular kind. The antibodies are so specialized they will be effective only against one particular antigen, so even after the antigen has been destroyed, tests of the specific antibody retained in the body for possible future use will allow identification of the antigen for which the antibody was made. Thus a blood test which discloses the presence of a certain antibody may indicate either the presence of its associated antigen (such as a virus) or that it has been present but now destroyed.

T lymphocytes are so named because they are special products of the thymus gland, and it is from the observations of T cells that the condition of the immune system can be assessed, as for instance in AIDS. Another indicator of immune potential is the total number of white cells in a cubic millimetre of blood, normal being considered 5000 to 7000, perhaps as high as 10,000, this higher figure being an indication of a toxic system. It is normal for numbers to increase with activity, stress or challenge by antigens, but sometimes greatly increased numbers will indicate toxicity tending towards leukemia.

Inflammation and fever are another response of the immune system and may occur locally at an area of infection or as the raised temperature of the entire body. As all vital functions in the body are brought about by enzyme activity, and as enzyme activity is greatly increased with increased temperature, fever which accompanies infection is an indication of good immune response. Often accompanying infection is swelling and soreness of the lymph glands nearest the seat of infection and this is an indication that the immune system is attempting to contain the infection where it is.

The capability of the immune system (immunocompetence) depends on the general state of health and physical fitness, but regardless of this may be drastically (but only temporarily) reduced in a healthy body by fatigue or excessive stress. The condition of the bloodstream is very important. When toxemia exists, and fat in the blood tends to stick blood cells and platelets into sludge, increasing blood viscosity and decreasing oxygen levels, the immune system along with the rest of the entire body becomes severely diminished in function. Thus various chronic disease conditions, such as cancer, are invariably marked by diminished vitality, low body temperature, low enzyme levels and low immunocompetence. Chronically ill people and senile people, therefore, more readily succumb to acute infection.

In particular, the level of immunocompetence depends on a healthy thymus, which in concert with the other endocrine glands directs the activities of the immune system. When health fails, or excessive demand is made on the immune system by way of infection or mental or physical trauma, the thymus, overworked, becomes exhausted, shrinks in size and loses function. Physical trauma includes toxemia, a great deal of which is produced within the body from wrong food, as previously described. Contributing to toxemia, however, are a great number of other substances harmful to the body and its immune system such as all drugs, medicinal or otherwise, antibiotics (refer to "AIDS" in Chapter 8), tranquillizers, pain killers, aspirin and so on, nicotine, marijuana, exhaust fumes, fluoride and chlorine, etc in water supplies. And to repeat, it is a fact that mental trauma alone, such as the pronouncement of cancer or AIDS, is capable of sealing a sick person's fate in a fashion like that of the bone pointing ritual of Aboriginals or the decree of death by a tribal witchdoctor.