PARASITES AND THEIR DEVELOPMENT. 



559 



come fully developed, would produce young in 

 large quantities, and would inflict upon the di- 

 gester of human tissue pain3 and grievances 

 compared with which the proverbial troubles 

 which afflict the just are as nothing. 



Less to be dreaded than the trichina, but 

 more extraordinary in its habits, is the " Guinea- 

 worm," a well-known parasite, confined in its 

 distribution to certain portions of Arabia, to the 

 banks of the Ganges, and to Abyssinia and the 

 Guinea coast. From the latter locality the or- 

 ganism derives its name. The Guinea-worm 

 troubles not the internal economy of man, but 

 has, strange to say, a striking and persistent apti- 

 tude for locating itself under the skin of the legs 

 and feet. The interest with which the Guinea- 

 worm is regarded by naturalists and others is de- 

 rived from the fact of its curious life-history and 

 habits, and from the supposition that tbis para- 

 site represents the " fiery serpents " which so ex- 

 ercised the minds and tortured the bodies of the 

 ancient Israelites. This supposition is somewhat 

 strengthened by the knowledge that Plutarch, in 

 his " Symposiacon," quotes a remark to the effect 

 that " the people taken ill on the Red Sea suffered 

 from many strange and unknown attacks," and 

 that, among other worms, " little snakes which 

 came out upon them gnawed away their legs and 

 arms, and when touched, retracted, coiled them- 

 selves up in the muscles, and there gave rise to 

 the most insupportable pains." Making allow- 

 ance for a few exaggerations, such a description, 

 especially in its latter portion, applies very close- 

 ly to this curious enemy of man. In length the 

 Guinea-worm may vary from one to six feet, while 

 specimens of twelve feet in length are not un- 

 known. The body is cylindrical in shape, and 

 attains a thickness of about one-tenth of an inch. 

 Curiously enough, not a single male Guinea-worm 

 has yet been met with, all the known specimens 

 belonging to the opposite sex. The worm enters 

 the skin as a minute organism which possesses a 

 singular vitality, and which exists in its free con- 

 dition in muddy pools, in wells, tanks, and in 

 marshes. In all probability the young Guinea- 

 worm gains access to the skin through the sweat- 

 ducts. Once located within the skin, the animal 

 grows rapidly, and in about a year attains the 

 dimensions just given. Every traveler in the 

 East knows the Guinea-worm by repute, and has 

 witnessed the familiar operation performed for 

 its extraction. Ancient works on medicine con- 

 tain descriptions of this operation, and exhibit 

 drawings of the worm and of the appearances 

 produced by its tenancy in the skin. The sole 



aims of the operator are those of extracting the 

 parasite by gentle traction, and of avoiding the 

 infliction of any injury to its body. This latter 

 forms, in fact, the great desideratum of the opera- 

 tor ; since, if the body of the parasite be broken, 

 and a portion left still within the body of its host, 

 additional and it may be serious irritation is there- 

 by set up. The long and slender body of the 

 worm is accordingly wound slowly and carefully 

 around some object, and the negroes on the 

 Guinea coast are said to be dexterous and skill- 

 ful in the performance of this somewhat delicate 

 operation. 



Perhaps one of the most remarkable points in 

 the history of parasites is that which refers to the 

 geographical distribution of certain of their num- 

 bers. That parasites require to be provided with 

 certain appropriate conditions for development is 

 a fact already noted. Indeed, we may go much 

 further, and say that the conditions demanded for 

 the successful development of many of these ani- 

 mals are infinitely complicated, and are in many 

 cases of singularly curious nature. But it would 

 also seem that in their " distribution " over the 

 surface of the globe, and in their selection of cer- 

 tain countries or regions as especial spheres of 

 development, some parasites evince remarkable 

 traits of character. One of the best-known in- 

 stances of this fact is afforded by a species of 

 tapeworm, to which the somewhat uncouth — to 

 ears unscientific, at least — name of Bothriocepha- 

 lus has been given. This latter is a species of 

 " broad-headed " tapeworm, differing from its 

 common neighbors in several points. It is un- 

 questionably the largest or longest parasite which 

 invades the human territory, and may attain a 

 length of over twenty-five feet ; its average breadth 

 being about an inch or rather less. In a large 

 " broad-head," as we may call it, upward of four 

 thousand joints or segments may exist, and as 

 each joint — after the first six hundred — is capable 

 of producing eggs and embryos, this foreign neigh- 

 bor is seen to be fully as productive as its com- 

 moner relations. The most interesting fact re- 

 garding the " broad-head," however, relates to its 

 geography and to its exact range among the hu- 

 man populations of the earth. It is a tolerably 

 well-ascertained fact that our common tapeworms 

 may affect inhabitants of any climate, but the 

 "broad-headed" species affects a singularity in 

 its distribution in that it has never been known 

 to occur outside the European province — that is, 

 it has never been found in any other continent 

 save in such cases as those in which it has been 

 conveyed to other continents by European hosts. 



