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Nature and Symptoms of Infections

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NATURE AND SYMPTOMS OF INFECTIONS These poisons are usually of bacterial origin, whilst the true poisons (bites of snakes and insects) play only a very minor role. As a rule, we find the most important cause of infection among the bacteria. They act either mechanically (obliterating the blood vessels through their tremendous increase in numbers) or most frequently through the poisons they produce (toxins), which are secreted by the bacterial cell and which are peculiar to eaeh species (specific). The bodies of the bacteria contain similar poisons which are freed by their disintegration (toxins). Some bacterial poisons destroy the red blood corpuscles (Inemolysins), others again cause the red cells to conglomerate (agglutinins). When the bacteria enter the body they destroy some of its cells; the parts surrounding the port of entry make preparations to defend themselves through inflammation, the flow of blood in the neighboring blood-vessels is accelerated (active hyperaemia), the blood vessels and capillaries are dilated, but owing to the damage suffered by the blood-vessels the blood current is soon retarded in the centre of the inflamed area (passive hyperemia). The bacterial poisons attract the leucocytes (chemotaxis). These latter go to the walls of the blood vessels and migrate through them, and at the same time eonsiderable quantities of liquid will leak through the blood-vessels into the surround ing tissues (inflammatory infiltration, oedema); in the mean time the affected cells have been killed, partly through the action of the poison and partly through interference with their nutrition. The dead tissues are dissolved and. segregated, and regeneration takes place from the healthy surroundings.

According to the greater or lesser rapidity with which these processes take place, they will be either acute or chronic in character; according to the condition of the exudate from the blood-vessels being serous, fibrinous, or consisting of pus-cells, we differentiate between serous, fibrinous, and purulent inflammations. These local symptoms are accom

panied by general systemic symptoms. The protective powers of the body are awakened by the absorption of the bacterial poisons. In the blood we can observe the production of the protective apparatus with which we have been familiarized through the work of Ehrlich and Netschnikoff. The action of the bacterial poisons is neutralized and the bacteria themselves are killed by the formation of substances which dissolve the bacteria and antitoxins and through the cooperation of different substances (complement and amboceptor) which are either in solution in the blood or combined with its constituents. Through the formation of opsonins they lose their power of resistance against the leucocytes, which increase tremendously at the site of infection and arrive there by migration and take up the weakened bacteria and destroy them. These processes are accompanied by a rise in the body temperature—fever. This differs characteristically in the different kinds of infection. Its peculiar course, its high excursions and deep remissions, as well as the way in which it terminates, may be used as an aid in diagnosis.

If the system should not be able to localize the infection and to wall it off against the rest of the body, then the bacteria and toxins will inundate the body—general infection. The body tries to protect itself against this invasion by defensive measures which are accompanied by high fever; bodies which have been considerably weakened cannot put up a sufficient defence if the infection should be highly virulent, and they will soon succumb to the general poisoning (septieLemia of atrophic children without fever).