202 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



..irti. 



drop of water containing numerous Ancylostoma larvae. Within a few 

 minutes a burning sensation and a distinct reddening of the skin became 

 apparent and he found that the larvae had disappeared into the skin, 

 leaving their empty cuticular sheaths behind. An experimental repetition 

 upon the skin of a limb an hour before amputation disclosed the larvae 

 in the act of burrowing through the skin, their 

 entry being as a rule by way of the hair follicles. 

 The exact route from the skin to the intestine was 

 determined by experiments on puppy-dogs with 

 another species of Ancylostoma {A. caninum). It 

 was found that the larvae make their way into 

 the blood-stream either directly through the veins 

 of the skin or by way of the lymphatics. Carried 

 round the circulation they reach the lung and there 

 bore their way out of the blood-vessel into the pul- 

 monary cavity. From this they migrate up the 

 trachea or windpipe and thus reach the oesophagus 

 en route for the intestine. There is no reason to 

 suppose that the Ancylostoma of man differs in these 

 migrations from that of the dog. 



It is very surprising to find in an intestinal 

 parasite like Ancylostoma the existence side by side 

 of two distinct modes of infection, one of them the 

 simple method which we should expect in the case 

 of a parasite of the alimentary canal by ingestion 

 through the mouth, the other by the unexpectedly 

 roundabout route through the skin. The suspicion 

 suggests itself that in Ancylostoma we have to do 

 with a parasite which formerly inhabited not the 

 alimentary canal but the connective tissue, obtain- 

 ing access to it by boring through the skin, but 

 which has comparatively recently become a parasite 

 of the alimentary canal, not yet however having 

 had time to get rid entirely of its former habit of 

 entering the body through the skin. 

 After reaching the intestine, by whichever route, the Ancylostoma 

 rapidly reaches sexual maturity and the first eggs make their appearance 

 in 8-IO weeks. 



In localities where Ancylostoma is prevalent the obvious precautions to 

 take are (i) to avoid drinking or using for kitchen purposes water that 

 may possibly contain living larvae, and (2) to avoid letting the skin come 



Fig. 93. 



Ancylostoma duodenale, 

 S X 10. b, Projecting 

 flap ; c, chaetae ; inty in- 

 testine ; ph, pharynx ; 

 (, testU. 



