ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 77 



the view that cercarite taken into the mouth in drinking water may 

 adhere to the mucous membrane of the mouth, tongue and oesophagus, 

 and at once proceed to penetrate into the tissues. As in ankylostomiasis, 

 there is little doubt that the infection occurs through the skin in the 

 bulk of cases, but experiment shows that it may also l)e oral. 



The author points out some conclusions of his inquiry : —Transient 

 collections of water are quite safe after recent contaminations ; per- 

 manent collections of water, such as canals, are potentially dangerous 

 because of the presence of the essential intermediary host ; the removal 

 of infected persons from a given area would have no effect, at least for 

 some months, in reducing the liability to infection, as the intermediate 

 hosts discharge infective agents for a prolonged period ; infected troops 

 cannot re-infect themselves or spread the disease directly to others, they 

 could only convey the disease to those parts of the world wliere a local 

 mollusc could efficiently act as carrier ; infection actually takes place 

 both by the mouth and through the skin, recently contaminated earth 

 or water is not infective ; infection in towns is acquired from unfiltered 

 water ; eradication can be effected without the co-operation of the 

 infected individuals by destroying the moUuscan intermediaries. 



In a continuation * of his account of his investigations on Bilharzia, 

 Leiper deals with prevention and eradication. The life of the Bilharzia 

 outside the body may be divided into three periods : (1) That between 

 the passage of the egg into water and the entrance of the hatched 

 parasite into the mollusc ; (2) the stage of metamorphosis within the 

 mollusc ; and (3) that prior to the entrance of the free-swimming 

 cercaria into the human body after it has left the mollusc. It is 

 universally recognized that in Egypt under present circumstances it is 

 practically impossible to prevent the contamination of water with in- 

 fected urine and fteces. In order to break the life-cycle of the Bilharzia 

 worm one must find some simple means of destroying it during the free- 

 swimming infective stage, or of depriving it of its essential intermediate 

 host. The former is the line of attack suited to the conditions under 

 which bilharziosis is acquired in large towns ; the latter is applicable to 

 country villages and districts. If the unfiltered water of Cairo could be 

 stored for two days, or a day and a half, there is no doubt that it would 

 become practically free from danger as far as bilharziosis is concerned. 

 The cercaria^ do not remain alive for more than thirty-six hours. The 

 stored water would lose its heavy sediment which is of great manurial 

 value for gardens. Against this loss may be set the fact that, at present, 

 one-third of the 30,000 children born annually in Cairo become infected 

 with Bilharzia. 



In agricultural districts some means must be found to stamp out the 

 molluscs harbouring Bilharzia in the places where they congregate and 

 multiply. Periodic drying, treatment with ammonium sulphate, and 

 other methods are discussed. 



The cercarife move by looping along or by swimming. They crawl 

 rapidly over any surface by alternate use of the oral and ventral suckers, 

 the tail being dragged passively behind. When they swim, the tail and 



* Journ. R.A.M.C, August, 1915, pt. 2, pp. 147-81 (figs. 25-39). 



