304 



GENERAL BIOLOGY 



way through the soles of the feet of persons who go barefoot. Once 

 in the blood-stream they are carried along by it to the heart, thence to 

 the lungs, and many lodge in the windpipe from whence they are swal- 

 lowed, thus reaching the stomach and intestines. The larval forms here 

 attach themselves to the intestinal 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. 



The writer was recently told by a worker 



jBMfew JB m the medical corps of the army that more 



iF- ftj| than 75 per cent of the examined southern 



J^H^rV negroes showed hook-worm infection. 



It is of great importance to dispose of all 

 !*5t\ human faeces in rural districts, in mines, brick- 



yards, etc., so that the soil will not become 

 polluted. This will kill the eggs and thus pre- 



& vent hatching of the parasites. Strong sun- 



light seems to be quite effective in doing this 

 pH 

 BP^ 



The family Filariidae is also important 

 from a pathological point of view. 



Filaria bancrofti (Fig. 191) is a parasite 



Fig> (Tro m E1 "New n %1enLm an - in human blood. It is interesting to know that 



these parasites live in the lungs and larger 



arteries throughout the day and in the blood-vessels in the skin at night. 

 Mosquitoes, which are active at night, suck the blood of infected per- 

 sons and thus carry the infection. In fact, it was the knowledge of this 

 which led to the discovery of the malarial parasite's life-cycle. 



As the organism is placed in another person by the mosquito, after 

 the larvae have developed in that mosquito's body, they enter the 

 lymphatics and cause serious difficulties, probably by blocking the lymph 

 passage. If there is such a blocking, elephantiasis results. This is a 

 practically incurable disease in which the limbs or other portions of the 

 body swell to an enormous size, although producing little or no pain. 

 (Fig. 192.) In certain portions of the South Sea Islands almost a third 

 of the population is affected. 



Medical men speak of Filaria diurna and Filaria perstans. The first 

 of these differs from F. bancrofti in not having granules in the axis of the 

 body, and the second by having its embryos smaller (namely, about 

 200 microns) than the preceding. Only the embryos have been seen. 

 The embryos of F. Bancrofti are about 270 to 340 microns in length. 

 The adult is about 83 mm. long and the female some 155 mm. The tail 



