328 THE ROUND WORMS 



blades of grass or vertical sides of mines. They can live in this stage 

 for months, when moisture and shade are present, but are rapidly 

 killed by drying. 



This is the infecting stage in which the larvae bore their way into the 

 skin, which is the usual method of infection, or, occasionally, by enter- 

 ing the mouth on vegetables or otherwise. 



Looss thought that they entered the skin by way of the hair follicles but the idea 

 now is that they can bore into any part of the skin. It only requires a few minutes 

 for the larvae to enter the skin. From the subcutaneous tissues they effect an en- 

 trance into lymphatics or veins, go to the right heart, thence to lungs. From the 

 alveolar capillaries they pass into the pulmonary alveoli, thence up the bronchi and 

 trachea, to pass out of the larynx and then down the oesophagus to the stomach. 

 The larva loses its protecting sheath in the stomach and in a few days develops a 

 provisional buccal capsule. 



By the end of the second week, after another ecdysis, the larvae have grown to be 

 about 2 mm. long and 130 microns broad and in about four weeks become adults, usu- 

 ally in the jejunum, where, after fertilization of the females by the males, the giving off 

 of eggs begins. The adults attach themselves to the mucosa of the intestine, feeding 

 on the deeper structures of the mucosa, or on the tissues of the submucosa. Sambon 

 believes that the larvae can work their way into the jejunum without going there by 

 way of the trachea and oesophagus. 



By providing an exit to the trachea, Fiilleborn demonstrated that in dogs, in- 

 fected with the dog hookworm, great numbers of larvae poured out of the trachea. 

 In other dogs he stitched the oesophagus to the skin and noted larvae coming out of 

 these openings. In these dogs, with the ordinary channel obstructed, infection did 

 occur with, however, only a few worms, thus showing the truth of Sambon's views 

 but at the same time demonstrating the unimportance of such a route of infection. 



The mouth cavity of the embryo is about as deep as the diameter 

 of the embryo at the posterior end of the mouth cavity; that of Strongy- 

 loides is only about one-half as deep as the diameter. There is also a 

 globular expansion at the bottom of the mouth cavity with hook- 

 worm embryos while with Strongyloides ones the passage to the oesoph- 

 agus is funnel-shaped. Also the genital anlage of Strongyloides is much 

 larger than that of Ancylostoma. 



A temperature of iC. kills the eggs in twenty-four to forty-eight hours. After 

 moulting twice, it remains rather quiescent but still lying inside the discarded skin. 

 It reaches this stage in from four to fourteen days according to the temperature. 



The soil in the area of the hookworm-egg-laden stool becomes infested with these 

 larvae which will even climb up blades of grass. It is for this reason that children 

 with their bare feet are so liable to infection. 



Laboratory Diagnosis. As a matter of fact the diagnosis is almost invariably 

 made by finding hookworm ova in the faeces. The eggs are oval and thin-shelled 

 with a wide, clear, glassy zone separating the more or less segmented, granular 



