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VI. INFECTION AND REINFECTION. 



In the vast majority of cases, primary infection is due to 

 the patient swallowing the fertilised eggs of Oxyuris. These, 

 when deposited by the female, dry rapidly, and are so minute 

 and light that they may actually float or be blown about 

 in the air. They settle on various articles of food, especially 

 those of a vegetable nature. Hence fruit, salads, lettuce, 

 watercress, and all vegetables commonly eaten uncooked, 

 are particularly liable to carry the infection. In some cases, 

 it seems as if even cooking would not destroy the vitality of 

 the eggs, hence worms sometimes appear to be introduced by 

 eating carrots, cabbage and spinach, although they have 

 been boiled. 



Filtered and Polluted Water. 



Drinking water has been blamed, but many authors cast 

 doubt on this as a source of infection. They say that when the 

 eggs are immersed in water for any considerable time, they 

 swell up, as a result of endosmosis, and burst, and the embryos 

 consequently die before they can reach the human stomach. 

 But, though this statement appears to be true of filtered 

 water, it does not seem to apply to polluted drinking water, 

 the solid contents of which, undoubtedly, may contain thread- 

 worm eggs, fully capable of normal development. 



Worms Swallowed Whole. 



Being so extremely small, the threadworm is sometimes 

 swallowed whole, especially by children, as described in the 

 preceding chapter, and if such a specimen is a female, 

 infection, per se, may be caused in that way. 



Wholesale Infection of Families. 



It has been suggested that infection may also occur directly 

 from rectum to rectum, if a healthy person shares the same 

 bed with a sufferer from threadworms. It is well known 

 that the parasites frequently creep out per anum at night, 

 and the supporters of the hypotheses say, if a worm can creep 

 out of one rectum, what is to prevent it creeping into another ? 



