Text A. Immunity

Infectious diseases are known to be caused by the invasion and growth of microorganisms in the human body. Infection may result from direct contact with patients or from indirect one.

But the human organism is known to have a specific capacity of resistance against infection, which is called immunity, it being natural and artificial. Under various conditions it may be entirely lacking, it may be relative, rarely it may be absolute. A previous attack of an infectious disease produces a more or less permanent protection against its subsequent infection.

In the course of their growth in the body many pathogenic microorganisms produce virulent poisons or toxins, they causing the characteristic symptoms of a particular disease. To meet the infection the cells of the body produce a chemical antidote which is specific for this particular infection and is known as an antitoxin. If the patient can produce a sufficient amount of this antidote to neutralize the toxins before the vital organs are injured recovery occurs. If the human body had not this capacity we should suffer from all infectious diseases.

If the toxin can be isolated from bacterial cultures and injected into men an artificial immunity can be produced which results from the formation of antitoxin.

The cellular elements of the tissues also take an active part in the protection of the organism against the infection. The presence of any infection usually produces leucocytosis and bacteria in the tissues are surrounded by white cells or phagocytes which prevent the spread of bacteria destroying them.

If the reaction against invading bacteria is insufficient, vaccines may be injected subcutaneously to produce a more active resistance of the protective mechanisms of the body. Vaccines are employed not only to contribute to the treatment of a disease, but to establish an active artificial immunity.

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Text B. Symptoms of Diseases of the Liver and Bile Ducts	\|	Text A. The Origin of Infections

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