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U.S. BUREAU OF FISHERIES 



three Mason jars were prepared with special lids. These tops had the 

 center cut out and served to hold two disks of 200-mesh Monel metal 

 wire cloth between which was a layer of absorbent cotton. The cotton 

 excluded algae and hydra but permitted bacteria to enter the jar, 

 which contained sterilized twine. These jars were placed in the lake 

 near the test racks. At the end of two weeks a jar was recovered and 

 the contents examined. Many bacteria were found but no algae, 

 protozoa, or other larger plankton organisms (the name commonly 

 applied to freely floating forms of Ufe). At this time the strength of 

 the twine had decreased very httle. At the end of a month a second 

 jar was opened and examined. Several examinations showed nothing 

 but bacteria present, proving the Alter had done its work in excluding 

 larger organisms. The twine from the second jar was dried; it was 

 found to be so rotten that no tensile strength determinations were 

 made. 



FliiUHE 2. — Composite net shovviiitj (iilTereiices in fouling un if>i paiu'l iiimi- a iiound net. The strip 

 neare.st the fi.sherman's hand is tarred; the others are treated with cuprous oxide treatments 



From these experiments it was concluded that red slime did not 

 harm nets markedly, since the twine in the screened jars rotted quite 

 as fast in the absence of hydra as the other twine did in the presence 

 of these organisms. Experimentally, it is almost impossible to grow 

 hydra in the absence of bacteria, hence the effect upon cotton of red 

 slime alone was not tested. It is thought on the basis of the fore- 

 going experiments, that the only probable harm resulting from hydra 

 is the increased bacterial action caused by these organisms affording 

 the bacteria a safe place for growth. 



EFFECT OF BACTERIA ON NETTING 



Description of attacking bacteria. — In order to learn what part 

 bacteria played in the rotting of nets, some slime was taken from a 

 pound net and examined with the microscope. Numerous bacteria 

 were present and so steps were taken to grow these organisms in the 



