BIONOMICS 159 



and no Strongyloides intestinalis were present in the faeces 

 have failed to demonstrate this mode of development. 

 The experiments have been so numerous and so gener- 

 ally unsuccessful that the existence of a free-living sexual 

 form may be excluded. 



The fully developed embryos are found in moist earth 

 and in mud. They remain alive in water, but fall to the 

 bottom of the water, and are not therefore likely to be 

 taken up with drinking water. 



Infection of man occurs if the embryos are swallowed. 

 This probably happens most frequently from eating, or 

 mixing food with fingers soiled with earth containing 

 ankylostome larvae. 



Looss has shown that there is another method by which 

 infection takes place. He finds that the larvae can pene- 

 trate into the skin and through it, and in the case of the 

 allied parasites of dogs, Uncinaria trigonocephala, he 

 demonstrated the subsequent passage of the larvae into 

 the vessels and that they were carried in the blood to the 

 lungs. From the lungs they pass into the trachea and 

 down the oesophagus into the stomach. When the larvae 

 have reached this stage they are not destroyed by the acid 

 contents of the stomach and pass on into the duodenum, 

 where they undergo ecdysis and attach themselves to 

 the mucous membrane of the small intestine. Looss has 

 shown that the infection of man can take place in a 

 similar manner and the worms reach the intestine. A 

 certain amount of irritation of the skin is caused by the 

 entrance of these larvae, and it is suggested that the vesi- 

 cular eruptions on the feet and elsewhere " water itch" 

 (not " coolie itch") are due to the entrance of these larvae. 

 Looss has further shown that the ankylostome larvae 

 are soon killed by the addition of water acidified with 

 o'2 per cent, hydrochloric acid, which he takes as the 

 normal acidity of the contents of the human stomach. 



The acidity of the stomach may average 0*2 per cent, 

 during active digestion of proteid food, but it is below 

 this in persons not in good health, and often much below. 



