Page:Collier's New Encyclopedia v. 01.djvu/469

BACTERIA 379 BACTERIA range in size from 1-lOOOOOth to l-3000th of an inch. Some species have the power of active motion, and may be seen moving rapidly to and fro in the liquid in which they are growing. This motion is produced by flagella, which protrude from the body. Marvelous Multiplication. — They mul- tiply by simple division or fission. Each individual elongates and then divides in the middle into similar halves; each of which then repeats the process. With some species the individuals remain attached after division, forming long chains; others produce solid groups of fours, eights, or sixteens. Some species that have been carefully watched under the microscope have been found, under favorable conditions, to grow so rapidly as to divide every half hour. At this rate in one day each microbe would produce over 16„000,000 descend- ants. At the end of the third day they would number millions of millions, the bulk and weight of which would be enormous, were it not that their rate of multiplication is checked either by lack of food or by the accumulation of their own excreted products, which are injurious to them. Harmful Bacteria. — Bacteria abound in all putrescent or fermenting mixtures containing organic matter, and are the cause of fermentation and putrefaction. Some are present in, and the cause of, certain of the zymotic or ferment diseases, such as malignant pustule, erysipelas, tuberculosis, etc. Micrococci are spheroidal bacteria, and very small, never more than l-25000th of an inch in diameter, often less. If they are kept out of surgical wounds, there is no sup- puration. The discovery of this fact made hundreds of operations possible which of old were thought to be out of the I'each of art — hence the wonderful success of antiseptic surgery. Bacillus Tuberculosis, — Very great interest attaches to the bacillus tuber- culosis, which is so constantly present that it is used as a means of differen- tiating the inflammatory diseases of the lungs from tuberculosis. This organism always produces the disease when Inoculated into animals. Statistics have been published showing that the bacillus was present in 2,417 out of 2,509 cases of supposed tuberculosis. Useful Bacteria. — In many respects bacteria are man's greatest benefactors; for upon their activities is founded the continued life of the animal and vege- table kingdoms. As microbes consume the material which serves them as food they produce chemical changes therein, resulting in simpler products called decomposition or cleavage products. Sometimes, however, they possess the power of building other compounds out of fragments, thus building up as well as tearing down. There are various industries based upon the decomposition powers of bacteria — viz., the maceration industries — in the separation of the valuable fibers from the useless fibrous material in the preparation of linen, jute, hemp, and cocoanut fiber; also in the commercial preparation of sponges, and often in the early stages of leather preparation. Some 50 years ago it was found that the mysterious substance known to brewers as yeast or barm was really composed of a vast number of minute oval particles that are endowed with the powers of growth and multi- plication, and, therefore, undoubtedly living. Bacteria in the Dairy. — In the ma- jority of butter-making countries the cream is subjected to a process known as ripening or souring before it is churned; the cream is allowed to stand for from 12 to 17 hours, thus giving the bacteria an opportunity to grow in it. As a result the cream becomes some- what soured, slightly curdled. Then the cream is churned. Not only does the ripened cream churn more rapidly and give a larger yield of butter than the sweet cream, but there are devel- oped the peculiar flavor and aroma which are characteristic of the highest product. The dairymen in the great butter producing countries of northern Europe are making practical use of this knowledge and are utilizing pure cul- tures of certain bacteria which have been found to be advantageous for the purpose of cream ripening and the production of agreeable flavors. Nitrifying Bacteria. — Everywhere in fertile soil is a class of bacteria which has received the name of nitrif jring bac- teria. They feed on the soil ingredients and have the same effect on the simple nitrogen cleavage products the vinegar- producing species have on alcohol — viz., bringing about a union with oxygen. Thus these nitrifying organisms form the last link in the chain that binds the animal kingdom to the vegetable king- dom. For the nitrates are left in the soil, and may now be seized upon by the roots of plants and begin once moi-e the journey around the food cycle. In this way it will be seen that while plants, by building up compounds, form the connecting link between the soil and animal life, bacteria in the other half of the cycle, by reducing them again, give us the connecting link between animal life and the soil. The food cycle