ANKYLOSTOMIASIS 145 



of two pairs of curved teeth attached to the ventral 

 edge in the Ankylostome, whilst in Necator there are no 

 teeth, only thickening of this edge of the capsule. The 

 genital opening in the female 4s behind the middle line 

 in Ankylostome and in front of it in Necator. 



In the male the rib supporting the mediodorsal lobe of 

 the caudal bursa, the dorsal ray, is of special importance. 

 In N. americanus it divides near the base and the tips of 

 each branch divide into two. In A. duodenale the dorsal 

 ray divides more than half-way up, and the tips of each 

 division divide into three (fig. 64 and A and B.) 



Geographical Distribution. The disease occurs in most 

 tropical and subtropical countries amongst those who 

 work on ground contaminated with the evacuations 

 of persons harbouring these parasites. It is therefore 

 common on sugar estates, amongst those occupied with 

 public works, roads, railways, &c., and amongst miners. 



Further north, as in England and the North of Europe, 

 it only occurs amongst those working in underground 

 mines, as the temperature on the surface of the earth is 

 not sufficient for the development of the worm. 



No race is exempt, but the conditions of life for 

 Europeans in the Tropics are such that the liability to 

 infection is slight. The disease occurs in all the conti- 

 nents and in most of the islands in the Tropics. In many 

 places, either directly or indirectly, it is a cause of a large 

 proportion of the total mortality. 



Clinical Course. The onset of the progressive anaemia 

 is insidious ; frequently it commences shortly after con- 

 valescence from some other disease, such as dysentery 

 or malaria. In other cases there may be febrile symptoms 

 in the early stages, but often there are no symptoms at all. 

 The patient notices increasing breathlessness on slight 

 exertion, and debility, and is found on examination to be 

 markedly anaemic. On plantations the money he earns 

 becomes steadily less. 



This anaemia steadily increases so that the patient 

 becomes breathless on the slightest exertion and utterly 

 10 



