276 THE ROUND WORMS 



undergo a third moulting. They then work their way up the trachea to the glottis 

 and are swallowed to then become adults in the intestine. Dr. Stiles, while accept- 

 ing this theory of the life history, thinks it probable that infection is also brought 

 about by swallowing directly some infecting stage. 



Very young dogs can be infected with human hookworm larvae, but infection of 

 man with the dog hookworm (A. caninum) has not been reported. 



The infecting stage is not a young larva but one in which the cuticle 

 of a former larval stage instead of being cast off remains and acts as a 

 protecting sheath for the more mature larva within. In this stage 

 larvae may remain alive for six to twelve months and have greater 

 powers of resistance than younger larvae. Introduction, either by skin 

 or mouth, of these cuticle-covered larvae is followed by finding of eggs in 

 the faeces in about fifty days. 



It has been claimed that where ordinary microscopical examination for ova will 

 show 40% of infections and methods involving concentration 55% that cultural 

 methods will show 99%. A convenient method of culturing is to make a pile of 

 filter-paper circles of 2 inches diameter and about 1/4 inch high and place in the center 

 of a 4-inch Petri dish. Fill the dish with water about to the height of the filter-paper 

 and spread a thick layer of faeces on the top of the filter-paper island. The larvae 

 hatch out in about six days and swim out into the clear surrounding water. They 

 are best found by centrifuging the fluid containing them. 



Of the three standard drug treatments that of thymol seems to be preferable 

 to betanaphthol and vastly so to eucalyptus oil. In giving thymol it is imperative 

 that neither alcohol in any form nor fats in any form be given on the day of treatment. 

 Stiles prefers to divide his thymol into three doses, 1/3 at 6 A.M., 1/3 at 7 and 1/3 

 at 8 followed by epsom salts at 10 A. M. The patient should be on a restricted 

 diet and be given two doses of salts on the two days preceding the administration 

 of thymol. 



Necator americanus. This is the species of hookworm found in 

 the southern states of the United States and the West Indies. 



It is very prevalent in Guam, L. I. It was found by Looss in pigmies from 

 Central Africa, so that this parasite was undoubtedly brought to America by slaves. 

 It is not rare in Ceylon, India and the Philippine Islands. 



The copulatory bursa of this parasite has double spicules which fuse terminally 

 in a barb, while A. duodenale has two fine hair-like spicules. The head of Necator 

 has a more marked dorsal bend than Ancylostoma. 



To sum up the differences between this species and A. duodenale 

 we have with Necator: i. Smaller oral cavity which shows rib-like 

 projections leading to the two ventral plates instead of the four promi- 

 nent projecting teeth. 2. The dorso-median ray of the caudal bursa is 

 deeply cleft and shows bipartite divisions terminally instead of having 



