NET DETERIORATION IN LAKE ERIE 



161 



where measured quantities of the water were introduced into tubes 

 containing Dubos medium and cotton gill thread. The subsequent 

 deterioration of this gill thread week by week is shown in Figure 9 

 which shows the results of weekly determinations of the tensile strength 

 of the thread. The history of one sample shows the large amount of 

 bacteria found in slime, which must therefore be considered a most 

 dangerous source of contamination to clean nets. It is to be noted 

 that contamination can take place far from shore and in water as deep 

 as 10 fathoms. The bacteria attacking the nets are apparently found 

 in all locations in the lake, but occur in largest numbers near shore, 



i.s 



ijd 



GmPHICAL PRESENTATlon^ 



0FF£5ULTS OF £XPEI?1MENTS 



BfVaking Strength of Tvvine 



A- Sterile Control -° — » — ' 



- B-lnoc.: Ice Slirtie, 4fni ot/t, 6F 



C-lnoc.'tcc. V\later,4'ni out, 6F 



P-lnoc-lcc Water^lSmi.euTjOF 



K 



N 



10 ZO 30 



ftrrte in Da^s 



Figure 9.— Breaking strength of twine 



40 



50 



where the water may contain as many as 500 per cubic inch. They 

 are most numerous in the slime found on nets or similar anchorages 

 and least frequent in the open lake, where their food is not as easily 

 available and agitation of the water is less marked. 



The remaining portion of the lake water collected from known 

 locations under aseptic conditions was used for determinations of 

 reaction and dissolved oxygen, given in Table 2. Note that the 

 oxygen content expressed here in parts per million, is high and rela- 

 tively uniform. This and the high temperature of the water is due 

 to the shallowness of Lake Erie. 



