3 ECONOMIC ZOOLOGY 



begun to migrate it may be arrested by use of calomel and other 

 purgatives, but after the worms are in the muscles there is no treatment 

 that will affect them. 



The death-rate has varied in different outbreaks from i to 30 per 

 cent. In America the disease is comparatively rare and is largely con- 

 fined to foreign-born people who make a practice of eating raw ham, 

 sausage, etc. In certain German States where this practice is very 

 common the disease is proportionately more prevalent. As a sure 

 preventive it is simply necessary to thoroughly cook all pork. It is 

 said that the centre of a large piece of fairly well cqoked pork may con- 

 tain live cysts and that salting does not always kill them. Pork from 

 private slaughter houses is more apt to be infected. The fact that pork 

 is marked "U. S. Inspected" does not guarantee it to be free from 

 trichinella. 



Filaria is a genus of small (less than i mm.) round-worms causing, 

 in man, various diseases. One curious fact about certain species is 

 that they are found in the human blood at night but not during the 

 day, or at least in very much smaller numbers. In a case where a 

 patient reversed his habits and slept during the day the parasites also 

 reversed their habits and were found during the day. How the 

 parasites enter the blood is not certain, probably by the bite of 

 a mosquito, possibly through drinking water. It is often very common 

 in the tropics. One of the diseases probably due, at least in some cases, 

 to this parasite is elephantiasis, which causes enormous and incurable 

 enlargements of the limbs and other parts of the body. There seems 

 to be no drug that will destroy this parasite in the blood. 



Guinea-worm (Dracunculus) is one of the largest of the round- 

 worms, reaching a length of nearly a meter. The larvae live in a water 

 flea, Cyclops, and probably gain access to the human digestive tract 

 in drinking water. Here they mature and the male dies and is voided. 

 The female, after being impregnated, leaves the intestine and becomes 

 fully developed in the subcutaneous tissue. She contains large numbers 

 of embryos and to get these to the exterior she migrates downward 

 into the leg, usually reaching the foot, where the head punctures the 

 skin, forming a small vesicle which ruptures and allows the embryos 

 to escape. The worm may then leave the body spontaneously or 

 it may be carefully withdrawn, care being taken not to rupture it. 

 It is sometimes the custom to wind the extruded end on a small stick 



