ANCYLOSTOMA AND STRONG YLO1DES 327 



branch instead of the shallow cleft and three stumpy processes of the two branches as 

 in A. duodenale. 



Goeze found a hookworm in a badger in 1782. He named the parasite Ascaris 

 criniformis. Froelich, in 1789, found hookworms in the fox and called them hook- 

 worms from the hook-like ribs of the copulatory bursa. He proposed the generic 

 name Uncinaria. Therefore Uncinaria belongs to the hookworms of the fox and 

 is not valid for any human species. 



In 1838, Dubini found a hookworm as a human parasite. On account of the 

 four ventral teeth projecting from the mouth he gave it the name A gchylostoma or 

 correctly Anydostoma. 



Bilharz and Griesinger noted the connection of the parasite with Egyptian 

 chlorosis, but it was not until the time of the St. Gothard tunnel (1880), that the 

 importance of the parasite was recognized. Grassi noted the diagnostic value of 

 the ova in faeces in 1878. In 1902, Stiles noted and described the hookworm found 

 in the United States as different and proposed the name Uncinaria americana, later 

 changed to Necator americanus. A. J. Smith had also recognized the morphological 

 differences. 



Hookworms may be found in the small intestine (jejunum) of man 

 in enormous numbers. They either produce their effects by feeding on 

 the mucosa or by causing loss of blood. 



Life History. The delicate-shelled eggs pass out in the faeces, and 

 in one or two days a rhabditiform embryo (200 X 14 microns) is pro- 

 duced. The mouth cavity of the embryo is about as deep as the diame- 

 ter of the embryo at the posterior end of the mouth cavity; that of 

 Slrongyloides is only about one-half as deep as the diameter. 



As a practical point, the anaerobic conditions in the intestines seem to prevent 

 development of the hookworm ova or at any rate the absence of the oxygen, so nec- 

 essary for the segmentations preliminary to the formation of the embryo, prevents it. 

 Therefore hookworm ova in freshly passed faeces never show other than commencing 

 segmentation while development of the larvae of Strongyloides takes place in the in- 

 testines, so that in freshly passed faeces we find, generally, actively moving larvae or 

 at least eggs containing fully developed embryos. Hookworm ova very rarely show 

 more than four segmentations or exceptionally eight in the freshly passed egg. 



In the presence of oxygen these ova rapidly develop into larvae, particularly at a 

 temperature of about 27C. Beyond 37C. and below i4C. development does not 

 seem to take place. 



The rhabditiform larvae grow rapidly and by the third day are about 

 300 microns long and undergo a primary moulting. By the fifth day 

 the bulb-like swellings disappear and the larva becomes possessed of a 

 straight oesophagus, thereby becoming a strongyloid larva. It then 

 undergoes a second ecdysis or moulting, but instead of casting off this 

 old covering, it retains it as a protecting sheath. At this time it ceases 

 to take food but can move actively in its sheath so that it can crawl up 



