304 



General Biology 



hook-worm disease, tropical 

 or Egyptian chlorosis, and 

 anaemia of bricklayers and 

 tunnel-workers. 



The old-world animal is 

 small and cylindrical, the 

 male being about 10 mm. in 

 length and the female from 

 10 to 18 mm. There are 

 chitinous plates about the 

 mouth and there are two 

 pairs of sharp, hook-shaped 

 teeth with which the mucosa 

 of the intestine is pierced. 

 On the male there is a prom- 

 inent caudal, umbrella-like 

 expansion. The American 

 species is slightly more slen- 

 der, with a globular mouth 

 and a different arrangement 

 of teeth. The eggs of the 

 American form are slightly 

 larger than those of the 

 European forms. 



The larvae of the hook- 

 worm develop in moist earth 

 and dig their way through 

 the soles of the feet of per- 

 sons who go barefooted. 

 Once in the blood-stream, 

 they are carried along by it 

 to the heart, thence to the 

 lungs. Many lodge in the 

 windpipe from whence they 

 are swallowed, thus reach- 

 ing the stomach and intes- 

 tines. The larval forms here 

 attach themselves to the in- 

 testinal walls and feed on 

 the blood of their host. But 

 as they puncture the intestinal wall, they exude a small amount of 

 poison which prevents the host's blood from coagulating. There is 

 thus a constant loss of tiny droplets of blood and the patient naturally 

 becomes anaemic. Not only do persons infected with hook-worm suffer 

 from such loss of blood, but the parasites injure' the lungs in passing 

 through them, and thus make tuberculosis infections easy. 



Forms of Worms Parasitic to Man. 



1. Larval stage of Filaria ozzardi (F. demarquayi). 



2. Larval stage of Loa loa (Microfilaria diurna). 



3. Larval stage of Filaria bancrofti (Microfilaria 

 nocturna.) 



4. Larval stage of Acanthocheilonema perstans (Mi- 

 crofilaria perstans). 



5. Adult parasite female of Strong yloides stercoralis. 

 6 ad 7. Adults, male and female, of the free-living 



generation of Strongyloides stercolaris. 



8. Rhabditiform larva of Strongyloides stercoralis, 

 just hatched from egg. 



9. Filariform infective larva of Strongyloides ster- 

 coralis. 



10. Rhabditiform larva of Ancylostoma duodenale, 

 just hatched from the egg. 



11. Filariform infective larva of Ancylostoma duo- 

 denale. (From Hegner and Cort's "Diagnosis of Proto- 

 zoa and Worms Parasitic to Man;" 1-4, after Fulleborn; 

 5-11, after Looss.) 



