RESISTANCE OF MATERIALS TO MARINE BIOLOGICAL ATTACK 1119 



scopic examination, there is also much degradation evident by the fungi. 

 Pin holes in the cell walls with associated fungal hyphae are extensive. 



Secondary cellulose acetate has been quite susceptible to microbio- 

 logical deterioration. Yarn has been destroyed in just six months of 

 marine exposure, not by borers, but predominantly by bacteria. Upon 

 microscopic examination, the fibers show severe surface erosion due ap- 

 parently to bacterial attack. In the marine samples which have been 

 stained and examined, hyphae have been evident in only one isolated 

 instance. The extent of the pitting and surface erosion in one of the 

 marine samples after one year in test can be seen in Fig. 10. This char- 

 acteristic pattern of erosion is also evident in samples of cellulose acetate 

 yarn from soil burial. Such a sample after 60 days of burial is shown in 

 Fig. 11. Here again attack appears to be predominantly of bacterial 

 origin. 



In the marine borer tests, the sample rods become heavily fouled in 

 the water area, as may be noted in Fig. 12. Although these fouling organ- 

 isms do not use the materials to which they attach as a source of food, 

 it is well known that they can do mechanical damage or chemically 

 influence the environment beneath them. The reader who is particularly 

 interested in the broad subject of fouling and its effect on materials, 



Fig. 11 — ("olhilose acetate after 60 days in laboratory soil burial. Note charac- 

 teristic surface erosion comparable to that shown in Fig. 10 for marine test sample. 

 Original magnification 500X. Photo by F. G. Foster. 



