Bacteria rule the world. Man is dep

Bacteria rule the world. Man is dependent upon them from the day of his birth until the hour of his death. They are man's most useful servants and his most destructive masters. One is prone to ask: What are bacteria? Where do they occur? What are their functions?

Bacteria are minute single-celled living beings devoid of roots, leaves and stems. They are so small that they can be seen only with the aid of a powerful microscope; They are often spoken of as microorganisms. This term includes not only bacteria but all forms of life so small that you should require the microscope in their study. They are often referred to as germs or microbes. The early investigators considered them animals and would refer to them as «animalcules».

If we examined the bacteria we should find that they have many of the characteristics of animals. Some have the power of independent motion. All are devoid of green colouring matter, chlorophyll; most of them are compelled to live upon complex foods as do the animals. Their general structure, their methods of growth, their formation of threads and spores, and their simplicity in some of the lower forms of plant life, have caused the biologist to class them as plants. However, it is impos-

sible to make a clear-cut1 distinction between some microscopical plants and some microscopical animals. The important thing to remember is that bacteria are the simplest forms of life, and partake of the characteristics of both plants and animals. For this reason, and for convenience, scientists agree to consider the bacteria with the plants.

Where do bacteria occur? Bacteria are widely distributed, occurring nearly everywhere. They are found in all natural soils, the number varying with the kind of soil, quantity of plant and animal debris present, moisture and treatment. They decrease in number with depth. Although they occur in air, it is not their natural home as under ordinary conditions they cannot grow and multiply in it. The number and variety found in air vary. The atmosphere of some high mountains and the air over the ocean far from shore may be free from bacteria. City and country air also differ from each other in the number and kind of bacteria which they contain. There is a great variation in the air of buildings. Bacteria are especially numerous where dust is plentiful.