NET DETERIORATION IN LAKE ERIE 163 



excellent home, since the currents passing by wash away waste 

 products and bring to the germs foodstuffs needed to supplement 

 the cellulose. Then, too, the interior of tbe cotton hber contains 

 nitrogenous material, always vital for life, btudy has shown that the 

 net-destroying bacteria found in Lake Erie are the type that can 

 live in the presence of oxygen but thrive best when only a small 

 amount of oxygen is present. Other cellulose-de^stroying organisms 

 Hve only in the absence of air, as in the case of those inhabiting the 

 soil and the digestive tracts of herbivorous animals, and hence do 

 not generally constitute a source of danger when washed into the 

 oxygen-bearing waters of the lake. . 



With the aid of general knowledge concerning bacteria and the 

 specific facts concerning these particular organisms it is possible to 

 describe briefly ways of fighting them. Inasmuch as bacterial growth 

 is greatly decreased or actually stopped by lack of moisture fouled 

 nets can be safeguarded by washing away most of their contamina- 

 tion and killing the rest by drying the net thoroughly. When sun- 

 light is available, its helpful rays add to the efficiency of the treat- 

 ment Unfortunatelv this simple though effective treatment can 

 be used only once in'a while. A second simple treatment is the use 

 of a strong brine solution. This kills bacteria by removing water 

 from their bodies. They shrivel in brine just as strawberries do 

 when much sugar is used for their preservation. Then, too alkaline 

 materials kill bacteria quickly. A clear lime-water solution may 

 be used on the nets to "cut the slime" and to stop bacterial action. 



Other germicides are known but they are generally rather expensive 

 for practical use and just as transient in their efl^ects as those which 

 are cheaper. Therefore, one finds it necessary to search for relatively 

 insoluble germicidal materials and finds that there are a number, of 

 which cuprous oxide, copper oleate, and mercuric oxide are cheap with 

 respect to their usefulness. ■ . a ,K+^^i,r 



These materials have been tried before ; copper resinate undoubtedly 

 wHl replace copper oleate because it has about the same solubility, 

 is cheaper, not as slippery, and is more adherent to the hbers. Any 

 other copper salt of an organic acid of molecular weight over 200 and 

 possessing no unsaturation will possibly serve as well, bince resin 

 acids constitute about 90 per cent by weight of rosm and since the 

 latter product is cheap, no further search for smtable copper salts 



seems necessary. , ^ • +v,„^„„k „ 



Cuprous oxide must be finely ground, 95 per cent passing through a 

 screen having 350 meshes per lineal inch, and may be further improved 

 in evenness of application and in the slow-settimg nature of its mix- 

 ture by grinding still finer, as m a colloid mill. . 



Tars are effective as germicidal treatments until the active^mgredi- 

 ents wash out, which probably takes place m two ^^n^l^^ liter 

 which thev offer mechanical protection only. The use of tar has been 

 abandoned in the work undertaken by the bureau's technologists 

 except as a "vehicle" to hold the toxic material upon the hber. 



TESTS OF PRESERVATIVE TREATMENTS IN THE LABORATORY 



Laboratory experiments were made in order to test net-preserva- 

 tive treatments rapidly and under rigorously controlled fonxiition^^^ 

 It was reahzed that factors such as the leachmg out of toxic mgredients 



