Linton. — Fish Parasites and Public Health 23 



It is not necessary to discuss the possibility of man's 

 becoming the secondary host, that is of harboring cestode 

 parasites in the encysted stage, as, even where such pos- 

 sibility exists, which is certainly not true in the case of 

 the butterfish cestode, infection would not be incurred 

 from using fish as food. 



It is interesting to note that the percentage of butter- 

 fish having considerable numbers of cysts in the flesh 

 has been diminishing in the Woods Hole region during 

 the past six years. The percentages of butterfish with 

 numerous cysts in the flesh for the years 1909-1914, in- 

 clusive, are 48, 29, 36, 15, 13, and 12 ; the smallest num- 

 ber of fish examined in any one year was 416, in 1910, 

 and the greatest was 948, in 1912. The results of the 

 examinations this year thus far show a rather marked 

 diminution in the number of parasitized fish from that 

 of last year. 



Trematodes. — Fortunately trematode parasites are not 

 at all common in fishes in situations which render them 

 liable to be ingested with parts used as food. In marine 

 food fish I have not found them in the flesh, although 

 they often occur in small cysts on the skin and especially 

 on the fins. They may be recognized as small specks of 

 black pigment, sometimes, especially on the cunner and 

 tautog, in large numbers. As fish are ordinarly pre- 

 pared for the table, such encysted trematodes are re- 

 moved. There is nothing unpleasant in the sight of these 

 skin parasites, unless they occur in very great numbers, 

 not a usual happening, and nothing is to be feared from 

 them, so far as at present known, even if they be eaten 

 uncooked. The natural final host of those whose life his- 

 tory has been made out is some fish-eating bird. Fishes in 

 fresh water lakes are more liable to infection in this way 

 than are the fishes of the sea. 



Nematodes. — Parasites of this order are found in the 

 alimentary canals of many species of marine food fishes, 

 especially in some of the larger kinds, such as the sword- 

 fish, cod, haddock, etc. They are also found encapsulated 



