FOULING OP SHIPS' BOTTOMS 237 



proper seasons and in favorable waters, with the exception of certain algse. However, 

 not all algae are free from such attacks. Darwin records the occurrence of a special 

 form of barnacles grown on the southern coast of Africa, and the author has found 

 another variety growing in abundance on the fucus on the breakwater at Beaufort, 

 N. C. 



Nevertheless, the question of selective attachment of the larvse of barnacles has 

 proved a fascinating one for experimental work. Knowing that barnacles attach 

 while in the cyprid stage, by means of an adhesive secretion thrown out from the 

 tip of the antennae, the possibility of finding some substances to which this "glue" 

 would not adhere presented an interesting phase of the problem. 



It has been found that the larvae of certain barnacles {Ohelonibia testudinaria) 

 attach only to the backs of turtles; others (C?i.eloniiia patula) to the shells of crabs; 

 others {Dichalaspis mulleri), again, to the gills and in the giU chamber of certain 

 species of crabs; and that one type of barnacle (Balanus gdleatus) grows only on a 

 special kind of coral. Likewise, other barnacles are found only above low tide line 

 (Balanus ialanoides) , and others, again, only helow low tide line (Balanus crenatus). 



Considering these possible factors, and especially the relation of the adhesive 

 substance of the barnacles to the nature of the surface to which it attaches, some 

 experiments have been made, using more than 12 different compounds, including 

 several decoctions made from different marine algse and which show conclusively 

 that no barnacle can attach to these films (at least within three weeks) during a 

 heavy "setting" period, when all other surfaces were being coated with young 

 barnacles. 



It is also of interest in this connection that the presence of a slime film on the 

 experimental panels, as well as on ships' bottoms, has been considered by some to 

 be advantageous in preventing fouling, while others take the opposing view. Recent 

 work done at the University of Washington by Miss Hillen (1923) would indicate 

 that this slime is of bacterial composition, and she even maintains that "without 

 this slime the barnacle would not settle upon the object (test panel) or develop upon 

 it, as the slime is used as food material for the young barnacle in its first development." 

 Further evidence on these points seems to be needed. 



METALS 



Different metals have been used as a means of preventing fouling since early 

 times, as was described in the iatroduction to this paper. Copper and zinc were 

 used abimdantly on wooden ships, but with the adoption of steel vessels the use of 

 these metals created electrolytic action that proved disastrous to the iron. 



That copper has a protective function toward certain growths is seen from the 

 record of the Denver (March 16, 1923), Cleveland (April 10, 1921), and the PJialarope 

 (August 19, 1923), all of which are wooden ships that were partially or completely 

 plated with copper sheathing. On these vessels barnacles were found as abundantly 

 on the copper as elsewhere, but algse and hydroids were conspicuously absent. Bry- 

 ozoa and serpuhds were present occasionally, but were not nearly so prevalent as on 

 the propeller blades and the struts, which were of alloy composition, probably 

 bronze. This difference was often noted on the propeller blades of iron ships, as on 

 the Florida (March 15, 1923), where a very dense growth of hydroids covered the 

 entire bottom but none were present on the propeller blades. 



