TraufiinisHioii 43 . 



brought back from Egypt four mice, twenty-six white rats, sixteen 

 desert rats, two guinea-pigs, and four mangaby monkeys, which 

 had been submitted to infection shortly before departure. When 

 examined shortly after their arrival in England all these animals 

 had enormous numbers of bilharzia worms in the portal system. 



Effect of Weak Acid and Alkali on Living Miracidia 

 AND Cercaria. 



The theory that Bilharzia infection takes place through the skin 

 was put forward by various South African writers from Harley to 

 Brock, because in their clinical experience infection was found to 

 follow repeatedly upon bathing in heavily contaminated waters. 

 Looss, on the other hand, adopted the view because weak acids 

 were found to kill the miracidium and consequently this, his 

 hypothetical infective agent, could not survive in the stomach 

 when taken in drinking water. The favourable action of weak 

 alkalis and the destructive effect of dilute acids on all cilia is one 

 of the recognized exercises in practical physiology. That alkalis 

 and acids should have a similar effect on the ciliated body of the 

 miracidium may be regarded therefore as a foregone conclusion. 

 It does not necessarily follow, however, that the same result 

 would obtain in the case of cercaria which are covered with 

 a cuticular skin. Experiments were undertaken therefore to 

 ascertain exact information on this point. Looss and others have 

 shown that miracidia are killed immediately by a dilution of 1 in 

 2,000 of hydrochloric acid. Cercarise withstand hydrochloric acid 

 1 in 880 for five minutes; 1 in 500 kills Bilharzia cercaria 

 immediately. The acidity of the stomach would therefore inhibit 

 these cercaria. This does not exclude the possibility, however, 

 that infection may take place through the mouth. The ankylos- 

 tomes and strongyloides infect through the mouth as well as through 

 the skin. Fiilleborn has recently shown that when the strongy- 

 loides are taken in by the mouth they do not pass on directly in the 

 lumen of the gut into the small intestine, but penetrate the wall 

 and, gaining the blood-stream, follow the circuitous route through 

 the lungs up the trachea and then pass for a second time down 

 the oesophagus through the stomach to the small intestine. 



Mode of Entry of Bilharzia into the Body. 

 That something similar to this might occur in Bilharzia was 

 suggested by a simple observation on the habits of the Bilharzia 

 cercaria. These cercaria progress by swimming mainly through the 



