29 



Hatching only possible in Human Stomach. 



After reaching its full development within the egg, it seems 

 that the embryo may live for a long time, awaiting suitable 

 circumstances for hatching. In addition to moisture and 

 warmth, which are the requisites for its development at this 

 point 1 , it appears proved that, normally, hatching is only 

 possible when the egg of the threadworm has reached a 

 human stomach, It is only there, and perhaps also within 

 the duodenum, that an embryo finds such natural conditions 

 as enable it to escape from the shell 2 . If the eggs happen to 

 be deposited by the female in any part of the intestine, hatch- 

 ing does not take place there ; they must be swallowed by 

 some human being before this can occur. Unlike many other 

 parasites, Oxyuris vermicularis does not have to pass any stage 

 of its existence in another animal, the so-called intermediate 

 host 3 . 



Growth and Maturity. 



Therefore, by some means or other, either with food or 

 otherwise, the developed ova must be swallowed by a human 

 being. Arrived in the stomach, the embryos almost at once 

 escape from the ova, when they are tadpole -shaped at first. 

 They quickly pass through the duodenum, jejunum and ileum, 

 and reach the coecum. On the way they grow rapidly, and 



" So verlangen die Eier von Oxyuris est limitee par une mince couche 



vermicularis eine Einwirkung von chitineuse. L'embryon est mobile 



32 R. Freilich entwickeln die Eier a 1'interieur de 1'oeuf, mais 1'activite 



der letzteren schon nach wenigen de ses mouvements depend de la 



Stunden, bei hoherer Tempera- temperature." (BLANCHARD, R., 



tur sogar in noch kiirzerer Zeit, op. cit., pp. 712, 713.) 

 einen vollstandigen Embryo." 2 Though hatching has been 



(LETJCKABT, R., Die menschlichen brought about artificially in saliva 



Parasiten, Leipzig, 1870, p. 73.) by some observers, in nature the 



1 Measurements of the embryo gastric juice solely performs this 



have been made: " Quand son de- office : " Un embryon gyriniforme 



veloppement est acheve, 1'embryon . . . ne peut continuer son devel- 



est long de 140 /u, dont 21 u. sont oppement qu'autant que le sue 



occupes par la queue : sa largeur gastrique, en ramollissant la coque 



maximum est de 10 ^. L'extremite de 1'oeuf a contribue a le mettre en 



anterieure est arrondie et large de liberte. L'infestation n'est done 



8 /< ; la queue est un cone effile, possible que si 1'oeuf est ramene dans 



large de 5 /j. a la base. Le tube 1'estomac au bout d'un temps 



digestif se voit distinctement a variable." (BLANCHAKD, R., ibid. 



travers la paroi du corps : 1'oeso- p. 721.) 



phage, long de 42 u, s'elargit en ? " Intermediate host not re- 



poire a son extremite, mais est en- quired." (COBBOLD, T. S., Human 



core depourvu de dents; sa lumiere parasites, London, 1882, p. 56. 



