CHAPTER III - THE BIOLOGY OF BACTERIA

Abstract

Bacteria are present wherever there is dead organic material; they are widely distributed in nature, being found on the surfaces of the body, in soil, dust, water, manure, and the air. The majority of bacteria are not restricted in their distribution, as they are able to survive and multiply under simple conditions; others can only grow under special circumstances and their presence in any vicinity is governed by the local conditions. Bacteria have been classified according to their growth requirements into two indefinite groups. Bacteria that normally grow at the expense of dead organic matter have been termed “saprophytes.” A small number of bacteria multiply under natural conditions only in the body-tissues and have been called “parasites.” These terms are only relative; it is impossible to separate one group from the other. Under some conditions, a parasitic organism might lead a saprophytic existence and vice versa. Some bacteria, such as the gonococcus and the influenza bacillus, are strict parasites and multiply in nature only in the tissues of the host; other parasites are found not infrequently growing under saprophytic conditions, and some bacteria, which usually multiply on dead material, are able to grow in the body-tissues. In all cases, growth can be obtained in vitro if a satisfactory culture medium is employed.