THE ASCARIS LUMBRICOIDES. 87 



Under conditions which have not yet been 

 satisfactorily determined, lumbrici may appear epide- 

 mically, or they may be endemically established in a 

 certain district. The writers of the last century 

 frequently refer to epidemics of fever or of dysentery, 

 connected with the presence of entozoa. 



When we endeavour to ascertain the conditions 

 which determine the rarity of the ascaris lumbricoides 

 in some localities, and its frequency in another, or its 

 appearance in a large number of cases, epidemically 

 as it were, it is especially requisite to recollect that 

 this entozoon proceeds from an ovum, and that 

 this ovum, after it has been expelled with the 

 evacuations, must again enter the human intestine 

 before it can become developed. It is consequently 

 necessary to find out how the ovum is conveyed into 

 the situation proper for its development. This is 

 done, says Dr. Davame, not by means of legumes, 

 nor of fruit, nor of bad diet, but through the medium 

 of the water which is used for drinking purposes. 

 The ova of the lumbrici are expelled with the evacua- 

 tions, which contain them in immense numbers. 

 These ova may remain in the waters of a marsh, of a 

 river, or of a well, during six or even more months 

 without undergoing any change ; the embryo which 

 becomes developed during this period is not set at 

 hberty until the ovum again enters the human intes- 

 tine. The use of a filter would separate the ovum 

 from the water ; exposure to a high temperature 

 would kill it. 



With these data, it will be possible to account for 

 the circumstance of these worms being so rare in 

 large cities, which have a properly regulated supply 



