PRESKRVATTON OF FTSH NETS. 5 



the solid food surrounding: it to liquefy, whereupon the liquid food 

 is absorbed. This di<rostive juice acts in a way simibir to that of the 

 human (li«restive juice, and i"or tlie same i)uri)ose; the i)rinci])al dif- 

 ference between our own dij^estion and that of bacteria is that ours 

 takes phice inside our bodies after the food is taken in, while the 

 bacteria dip:est it before. So after all there is nothing; incredible 

 about it. Most bacteria are equipped for usin^ a particular class of 

 foods — they are meat eaters, sugar eaters, starch eaters, fat eaters — 

 and they do not mix foods. They are able to secrete a dijjestive 

 juice capable of liquefyino; that particular food on which they live. 



Now, from what has been said, it is easy to see that the damage 

 done to nets by bacteria must be done in either one of two ways, viz, 

 the digestive juice itself or some of the changed products of digestion 

 must attack the nets or else the waste products thrown off from the 

 bacteria themselves (and some of these are active or virulent chemi- 

 cals) must do so. If the digestive juices attack the cellulose fibers of 

 the net, of course the fibers are dissolved, and this dissolution woidd 

 be a very effective rotting. At any rate, what has already been said 

 constitutes about all that can confidently be said about the intimate 

 nature of bacterial decomposition of nets. If any more is to be 

 known about it, a study must be undertaken. 



For preserving nets against bacteria a number of possibilities sug- 

 gest themselves. Since bacteria require water for activity, it is plain 

 that if we keep the nets dry as much as possible we lessen the de- 

 composition. But since the use of fish nets requires them to be wet, 

 another step may be taken against the bacteria. It is possible to 

 impregnate the fibers with substances that are poisonous to bacteria, 

 or, quite as effective, which spoil the activity of the digestive juices 

 produced by bacteria. Creosote and substances containing copper 

 have been used for this purpose. Another method of preventing the 

 destructive action of bacteria is to make the fibers insoluble and 

 proof against the digestive action of bacteria. For hardening the 

 fibers and making them harmful and indigestible to bacteria, tanning 

 barks and extracts, such as birch bark, catechu, quebracho, quercitron, 

 etc., have been used. These will be considered in detail later. Mean- 

 while other methods of resisting the action of bacteria are to cover 

 the fibers with a protective coating, such as tar, linseed oil, etc. 



OXmATION. 



Another enemy to nets is oxidation. The air consists of one-fifth 

 oxygen, a colorless gas, which supports all fire and also is the active 

 constituent of our breath. When one "sets fire to" a combustible 

 material one so heats a small part of the material that the oxygen 

 of the air combines directly with it. This combining releases more 

 heat, which in turn hastens the combining of more oxygen with still 

 more of the material, and so on, until the material is burning. While 

 most combustible substances either burn rapidly or not at all, some 

 things may oxidize slowly. For example, wdien nets are stored wet, 

 covered with herring oil, blood, and slime, all of which are easily 

 oxidizable, tlie oxygen of the air combines with these fish residues 

 and probably also with the net. A heating thus l)egins, and the nets 

 may even take fire; if not, the heat generated may be sufficient to 

 weaken or destroy them. 



