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.

Jute and Hemp.—­Almost exactly the same use is made of bacterial action in the manufacture of jute und hemp.  The commercial aspect of the jute industry has grown to be a large one, involving many millions of dollars.  Like linen, jute is a fibre of the inner bark of a plant, and is mixed in the bark with a mass of other useless fibrous material.  As in the case of linen, a fermentation by bacteria is depended upon as a means of softening the material so that the fibres can be disassociated.  The process is called “retting,” as in the