Linton. — Fish Parasites and Public Health 21 



The successful completion of the round of life of many 

 of these parasites requires that the host which harbors 

 one stage of the parasite be eaten by a host in whose 

 alimentary canal the parasite will find conditions favor- 

 able for its further development. As a rule the number 

 of species of animals which are fitted to become the final 

 host, that is the host in which the parasite becomes adult 

 and produces eggs, is limited. Thus in the case of the 

 flesh parasite of the butterfish, although the butterfish 

 is eaten by all the larger carnivorous fish that swim the 

 waters with them, they develop only in the sharks, and 

 in an exceedingly small number of species of shark. To 

 make the question still simpler, it may be said that when 

 a blue fish, for example, eats a butterfish that is harbor- 

 ing cestode cysts in the flesh, it utilizes as food the 

 cestode cysts with their contents in the same manner and 

 doubtless with equal benefit as follows the assimilation 

 of a similar quantity of proteid material from the mus- 

 cular tissue; while a hammerhead shark which eats a 

 butterfish containing these cestode cysts in the flesh, in- 

 stead of digesting the larva that will be liberated from 

 the cyst, furnishes the proper conditions for that larva 

 to develop, and he will have in a short time the adult 

 cestodes in his spiral valve. There is no reason to believe 

 that the butterfish cestode will develop in man; on the 

 contrary there is very good reason to believe that it will 

 not develop in any warm-blooded animal. Furthermore, 

 all helminth parasites are killed in ordinary cooking and 

 the tissues of which they are composed are doubtless as 

 nutritious as are those in which they chance to be em- 

 bedded. Again, the popular mind should be taught to 

 discriminate between the animal and vegetable inhabit- 

 ants of living animals and those which may make their 

 appearance in the flesh of animals after they are dead. 

 The latter, when they are the larvae of insects for ex- 

 ample, that is maggots, create unpleasant sensations arid 

 suggest spoiled meat, or meat that has not been properly 

 cared for; when bacteria, they are associated with the 

 disturbing phenomena of putrefaction. In either case 



