THE OXYURIS. 105 



been observed in Central Africa ; and Leidy says 

 that they are more common than any other species 

 of worms amongst the white inhabitants of North 

 America. 



The presence of thread worms is, perhaps, more 

 freqviently discoverable by pathological phenomena, 

 than that of the other intestinal entozoa. They 

 usually produce a feeling of irritation in the rectum, 

 lancinating pains, cramps, and acute, intolerable itch- 

 ing at the anus, or sometimes extending to the 

 genito-urinary organs. These symptoms are greatly 

 exacerbated at certain periods which vary according 

 to the individual who is affected, or, it may be, 

 according to the hours at which the meals are taken. 

 The patients are commonly most tormented at the 

 approach of night, and especially at bed time ; and 

 these sufferings return with such a degree of perio- 

 dicity as can be explained only by their evident 

 relation to the uniform performance of the digestive 

 functions. 



The patients are sometimes much depressed in 

 spirits ; and they suffer frequently from diarrhoea. 

 Their evacuations are often soft, fetid, and covered 

 with tenacious mucus, or streaked with blood. 



It is generally easy to ascertain that these symp- 

 toms are due to the presence of oxyurides ; some of 

 these worms may be found in the folds of the 

 sphincter ani, or in its immediate vicinity, and they 

 are also expelled, at intervals, with the evacuations. 

 Upon examination no cutaneous disorder is per- 

 ceptible at the margin of the anus, but the mucous 

 membrane which surrounds the sphincter is tumid, 

 red, injected with blood, and covered with a thick, 



