The work opens with an exhaustive examination of the schizomycetes, commonly known as bacteria, tracking their historical discovery from early microscopic observations by Leeuwenhoek to the systematic classifications established by Cohn and later biologists. The author details the minute single-celled structure, the presence of a definite cell-membrane, and the varying arrangements of cilia or flagella, which serve as organs of independent movement in motile species. The processes of cell division, vegetative growth, and the formation of zoogloea resting states are traced with precise measurements, illustrating how constant environmental conditions maintain regular doubling periods.
Attention is directed to the formation of endospores, which represent a highly resistant resting stage capable of enduring extreme temperatures and desiccation. The historical debates concerning spontaneous generation are reviewed, demonstrating that no putrefaction or fermentation takes place without living organisms. Pasteur's pioneering work on lactic and ammoniacal fermentations laid the foundation for the germ theory of disease, wherein pathogenic bacteria produce specific structural changes through the elaboration of toxic substances.
The volume explores the supreme importance of bacteria in agriculture and daily life, particularly in the circulation of nitrogen, carbon, and sulphur in nature. The mechanism of nitrogen fixation is explained through the symbiosis between nitrogen-fixing bacteria and the root nodules of leguminous plants, which enable the host to assimilate inert atmospheric nitrogen. Nitrifying bacteria oxidize ammonium carbonate in two distinct stages, first forming nitrites through nitroso-bacteria and subsequently nitrates through nitro-bacteria, thereby preparing primitive soil on barren rocks.
Further sections examine cellulose-decomposing bacteria in marshes, sulphur bacteria that utilize hydrogen sulphide as a respiratory substance, and iron bacteria that liberate energy by oxidizing ferrous compounds into ferric oxide. The physiological action of chromogenic and phosphorescent bacteria is detailed, alongside the bactericidal effects of blue-violet and ultra-violet solar rays. The work concludes with an extensive pathological analysis of bacterial infection, detailing the separation of extracellular and intracellular toxins, the nature of antitoxic and antibacterial sera, the mechanisms of phagocytosis, and the complex factors governing natural and acquired immunity in animal tissues.
