Chapter XVII — 195 — Economic Importance 



passage through the digestive tract of Teredo. The lignin content was de- 

 creased only slightly. However, it is still indeterminate whether the ccllu- 

 lases and lignases arc elaborated by Teredo or by commensal bacteria. 

 The gut of engorged Teredo as well as its burrows contain large numbers of 

 cellulose- and lignin-digesting bacteria. Conceivably the bacteria convert 

 the cellulose and lignin into products which are more readily assimilated 

 by the wood-borers. 



The bacteria themselves are nutritious. The number present at any 

 one time on the wood or in the gut of wood-borers is not enough to provide 

 for the complete requirement of the wood-borers, but the " standing crop " 

 of bacteria is not an adequate criterion. Considering that bacteria repro- 

 duce every hour or two under favorable conditions, the standing crop 

 multiplied by lo to 20 would be more representative of the amount of 

 bacteria available per day as food. 



Cellulose- and lignin-decomposing microorganisms may help to condi- 

 tion the wood for initial attack by wood-borers. The extensive degrada- 

 tion of wooden structures by fungi in the sea has been reported by Barg- 

 HOORN and Linder (1944), who observed a conspicuous softening in the 

 outer parts of pilings and submerged wood. The activities of such organ- 

 isms may help to explain why wood becomes increasingly more suscep- 

 tible to attack by wood-borers as its period of immersion is prolonged. 

 Given a sufficiently extended time, either bacteria or fungi could inde- 

 pendently effect the complete deterioration of wooden structures. The 

 rate, though, is far from being commensurate with the rapid destruction 

 of wood by Teredo or Lwmoria. 



Destruction of cordage and fish nets : — After periods of from three 

 to five weeks' immersion in the sea, textile fibers were found by DoRf e 

 (1920) to be completely rotten. Fabrics had become coated with a bac- 

 terial or diatomaceous film within a week after immersion. Cotton was 

 found to be less durable than linen or silk. Wool was the most resistant. 

 The deterioration was shown to be caused by microorganisms and not by 

 abiogenic oxidation, light, or salts. 



The deterioration of fish nets in Lake Erie was found by Robertson 

 and Wright (1930) to be due to cellulose-digesting bacteria. Both linen 

 and cotton lines, seines, and nets were attacked. According to Robert- 

 son (193 1), the value of fiber seines, nets, traps, and lines used by com- 

 mercial fishermen in the United States in 1930 was about $15,000,000. 

 Such equipment lasts an average of less than two years, its durability be- 

 ing affected primarily by the activities of cellulose-decomposing bacteria. 

 The usefulness of the nets, seines, and lines can be extended by applying 

 copper resinate and other preservatives. The tendency of certain pre- 

 servatives to decrease the flexibility, impart undesirable colors, or other- 

 wise adversely affect the properties of the fiber equipment complicates the 

 problem. 



Manila ropes and cotton nets were found by Atkins and Warren 

 (1941) to be destroyed after 14 months alternate wetting in sea water and 

 drying, as in ordinary use. Preliminary treatment of the fibers with cop- 

 per naphthenate was found to prolong the useful life of the rope by 

 40 per cent. 



The occurrence of fungi on the North Atlantic coast which infect cord- 

 age fibers, including hemp, jute, and sisal, causing deterioration under 

 marine conditions has been reported by Barghoorn (1942). Barghoorn 



