THE STORY OF GERM LIFE

CHAPTER II: MISCELLANEOUS USE OF BACTERIA IN THE ARTS.

The foods upon which bacteria live are in endless variety, almost every product of animal or vegetable life serving to supply their needs. Some species appear to require somewhat definite kinds of food, and have therefore rather narrow conditions of life, but the majority may live upon a great variety of organic compounds. As they consume the material which serves them as food they produce chemical changes therein. These changes are largely of a nature that the chemist knows as decomposition changes. By this is meant that the bacteria, seizing hold of ingredients which constitute their food, break them to pieces chemically. The molecule of the original food matter is split into simpler molecules, and the food is thus changed in its chemical nature. As a result, the compounds which appear in the decomposing solution are commonly simpler than the original food molecules. Such products are in general called decomposition products, or sometimes cleavage products. Sometimes, however, the bacteria have, in addition to their power of pulling their food to pieces, a further power of building other compounds out of the fragments, thus building up as well as pulling down. But, however they do it, bacteria when growing in any food material have the power of giving rise to numerous products which did not exist in the food mass before. Because of their extraordinary powers of reproduction they are capable of producing these changes very rapidly and can give rise in a short time to large amounts of the peculiar products of their growth.

It is to these powers of producing chemical changes in their food that bacteria owe all their importance in the world. Their power of chemically destroying the food products is in itself of no little importance, but the products which arise as the result of this series of chemical changes are of an importance in the world which we are only just beginning to appreciate. In our attempt to outline the agency which bacteria play in our industries and in natural processes as well, we shall notice that they are sometimes of value simply for their power of producing decomposition; but their greatest value lies in the fact that they are important agents because of the products of their life.

We may notice, in the first place, that in the arts there are several industries which may properly be classed together as maceration industries, all of which are based upon the decomposition powers of bacteria. Hardly any animal or vegetable substance is able to resist their softening influence, and the artisan relies upon this power in several different directions.

BENEFITS DERIVED FROM POWERS OF DECOMPOSITION.

Linen.—Linen consists of certain woody fibres of the stem of the flax. The flax stem is not made up entirely of the valuable fibres, but largely of more brittle wood fibres, which are of no use. The valuable fibres are, however, closely united with the wood and with each other in such an intimate fashion that it is impossible to separate them by any mechanical means. The whole cellular substance of the stem is bound together by some cementing materials which hold it in a compact mass, probably a salt of calcium and pectinic acid. The art of preparing flax is a process of getting rid of the worthless wood fibres and preserving the valuable, longer, tougher, and more valuable fibres, which are then made into linen. But to separate them it is necessary first to soften the whole tissue. This is always done through the aid of bacteria. The flax stems, after proper preparation, are exposed to the action of moisture and heat, which soon develops a rapid bacterial growth. Sometimes this is done by simply exposing the flax to the dew and rain and allowing it to lie thus exposed for some time. By another process the stems are completely immersed in water and allowed to remain for ten to fourteen days. By a third process the water in which the flax is immersed is heated from 75 degrees to 90 degrees F., with the addition of certain chemicals, for some fifty to sixty hours. In all cases the effect is the same. The moisture and the heat cause a growth of bacteria which proceeds with more or less rapidity according to the temperature and other conditions. A putrefactive fermentation is thus set up which softens the gummy substance holding the fibres together. The process is known as "retting," and after it is completed the fibres are easily isolated from each other. A purely mechanical process now easily separates the valuable fibres from the wood fibres. The whole process is a typical fermentation. A disagreeable odour arises from the fermenting flax, and the liquid after the fermentation is filled with products which make valuable manure. The process has not been scientifically studied until very recently. The bacillus which produces the "retting" is known now, however, and it has been shown that the "retting" is a process of decomposition of the pectin cement. No method of separating the linen fibres in the flax from the wood fibres has yet been devised which dispenses with the aid of bacteria.