464 THE ANIMAL PARASITES OF MAN 



in Finland, Greenland, etc. In temperate climates A. Inmbricoides 

 occurs most frequently in young children ; it is, moreover, more 

 common amongst country dwellers than amongst the inhabitants of 

 towns, but is not lacking in infants, adults and aged persons. As a 

 rule only a few specimens are present in the intestine, but many cases 

 are known in temperate zones in which several hundreds of worms 

 have been found in the same patient. This species is particularly 

 numerous in the negroes of Africa and America. It occurs also in 

 the monkey, dog and pig ( ? A. snilhi). 



The parasite was known in ancient times ; the Greeks called 

 it e'X/ui>9 <TTporyyv\r), Plinius termed it Tinea rotunda, ater on 

 it was named Lnmbricns teres. The aa-icapis of the Greeks is our 

 Oxyuris. 



The small intestine is the normal habitat of Ascaris lumbricoides ; the worms, 

 however, often leave this part of the intestine and wander into the stomach, whence 

 they are frequently evacuated by vomiting, or they may creep through the oeso- 

 phagus into the pharynx and crawl out through the nose or mouth ; very rarely they 

 may find their way into the Eustachian tube or into the naso-lachrymal duct, or into 

 the excretory ducts of the liver and pancreas ; exceptionally they may gain the 

 trachea, and they have also been found in the abdominal cavity. They may bore 

 through adhesions between the intestinal wall and the omentum (worm abscess) ; 

 they occasionally penetrate the urinary apparatus and are passed with the urine ; 

 in febrile diseases A. lumbricoides usually leaves the intestine spontaneously. It is 

 obvious that these wanderings may be accompanied by the most serious symptoms, 

 but in sensitive persons the invasion of even only a few intestinal Ascarides gives 

 rise to a series of almost inexplicable symptoms ... (hysterical, epileptiform attacks, 

 cerebral congestion, aphonia, etc.), which cease-with the expulsion of the worms, so 

 that many authors are driven to the conclusion that Jhese Acandes secrete a toxin. 

 Fortunately, the presence of A. lumbricoides in the intestine is easily demonstrated 

 by the microscopical examination of the faeces. 



Development. Several authors (Gros, Schubart, Richter, Leuckart 

 and Davaine) have demonstrated that the ova of Ascaris develop 

 in water or moist earth after a long period of incubation. Freezing 

 and desiccation (if not too long) do not injure their powers of 

 development ; the duration of the development depends on the 

 degree of the surrounding temperature. At a medium temperature, 

 after a varying period of incubation, it takes from thirty to forty 

 days for the embryo to become formed. The spirally rolled up 

 embryo, with its so-called " tooth," formed by three papillae close 

 together, never leaves the egg-shell in the open, even if the eggs are 

 kept for years under favourable conditions. Davaine proved that the 

 larvae hatch out in the intestine of the rat, but are again expelled with 

 the faeces ; he therefore concluded that the hatching likewise takes 

 place within the intestine of man, but is followed by the invasion 

 of the larvae. In the meantime Leuckart had sought to infect himself 

 by swallowing embryo-containing eggs, but without results ; he 



