BACTERIA

They are organisms of microscopic size whose effect on other living things is out of all proportion to their tiny size. Most bacteria are only about one-thousandth of a millimeter in diameter. They vary in length, but are too small to be seen with the naked eye. Without the help of this vast invincible army, all life grouped by the way they live. A few kinds make their own

food, but most of them live off dead or decaying matter (as saprophytes), or off living organisms (as parasites).

Saprophytic bacteria are extremely important to biology as decomposers. Dead animals and plants decay through the action of bacteria, which consume the organic parts and return them, eventually, to the soil. Without the aid of bacteria, energy would remain locked up in undecomposed dead matter accumulated since life began. Much bacterial decomposition is put to good use by man. He purifies sewage, produces cheese, cures tobacco, and prepares flax with their help. But, at the same time, other bacteria turn meat rotten, sour milk, and make butter rancid, while some obtain food energy for their own purposes. One of the most important contributions of bacteria is the part they play in making nitrogen available to plants. Nitrogen gas is abundant in the atmosphere, but animals and plants have no means of converting it into usable forms. However, certain kinds of bacteria that live in the soil or in the roots of legume plants such as clover and beans are able to convert nitrogen gas to nitrites and nitrates, which are eventually built up by plants into proteins.

Parasitic bacteria cause numerous serious diseases of man, including tetanus, tuberculosis, diphtheria and various kinds of blood poisoning. Before the use of antiseptics, these so-called pathogenic bacteria caused misery and death in colossal proportions, and rendered even the simplest surgery hazardous. Nowadays surgery is carried out in germ-free rooms. The development of antibiotics has also helped enormously in the fight against bacterial diseases. The picture shows some disease-causing bacteria, greatly magnified. Bacteria reproduce by the division of their single cell into two identical parts, and in favorable conditions new generations occur every twenty minutes. Some bacteria can move in water. They either wriggle about, or have whip-like hairs to help them ‘swim’.