CCELHELMINTHES 221 



invasion of the intestines of man by the thorn-headed worm of the pig 

 {Gigantorhynchus hirudinaceus) is regai'ded as stray or accidental, but 

 if the grub of the May beetle, the larval host of this worm, constituted 

 a choice morsel of diet for man as it does for the pig, it is probable that 

 the thorn-headed worm would much more frequently inhabit man's 

 intestines. 



Adaptive modifications from a free to a parasitic hfe, and adaptations 

 of the parasite to differing host environments, or to new locations taken 

 up in the body of the same host, are best exemplified in the Protozoa. 

 In the more complexly organized worms the faculty of adaptation is 

 possessed in less degree; though undoubtedly the parasitic forms have 

 without exception passed through at least the first of the gradations 

 mentioned. The adult nematodes infesting the respiratory tract, as 

 Dicfyocaulus filaria of sheep, and those infesting the blood vascular 

 system, as Dirofilaria immitis of the dog, have probably reached these 

 regions from a primary parasitism in a less obscure part of the body, 

 the adaptivity having become sufficiently fixed that the conditions 

 suppHed by the location later acquired are now specifically essential 

 to their sexual development and reproduction. 



Treatment in General. — Treatment in nematode helminthiasis has 

 in view primarily the expulsion of the worms, and secondarily the 

 building up of the general health of the animal. Anthelmintics act by 

 destroying or in some way so affecting the worms that they are easily 

 expelled from the body. An agent capable of killing the parasites may 

 have a like effect upon the host if used without due precaution; in any 

 event it is likely to be too drastic and cause an acute disturbance more 

 serious than the subacute one which it is sought to remedy. In the 

 case of intestinal worms, remedies which reduce them to a sufficiently 

 passive state that they may be readily swept out by the action of a 

 purgative are to be preferred; and here the effect of the vermifuge 

 upon the host, as compared with that of a true vermicide, is one 

 of degree, and the tolerance of the patient is to be taken into con- 

 sideration. 



Essentially the success of vermifuge treatment will be influenced by 

 the location of the worms; only those in tubular organs in communica- 

 tion with the outside can be reached by such medication, while its action 

 will be hampered in the case of those which burrow into and attach 

 upon the mucous lining. 



It has been said that it may be taken as an axiom in helminthology 

 that each worm in the body develops from an egg or larva which has 

 entered from without. Worms do not go on multiplying indefinitely 

 with the production of new adult generations in the same host. The 

 degree of the infestation, therefore, depends primarily upon the degree 

 of contamination of food or water taken in by the animal, and secondarily 



