244 



DISEASES DUE TO HELMINTHS 



THE LIFE HISTORY. 



The young immature male and female are only found in the portal 

 system from whence they go to the portal vein. Here they pair and 

 then pass to the liver. 



The male carries the female down along the portal and the inferior 

 mesenteric veins to the bladder. Here oviposition takes place and the 

 eggs are deposited in the superficial capillaries. From this position 

 they gradually work their way to the surface and enter the bladder itself. 

 Some of the eggs, however, become calcified in the process. 



If the eggs are taken from the urine and examined they will be seen 



Micrograms of sections of skin of a newly-born mouse which had been immersed for half 

 an hour in water containing large numbers of Bilharzia cercarise. 



to contain a living miracidium which can be liberated if the egg is 

 broken while imder the microscope. 



The eggs must pass to water at once or the miracidium dies. 



It does not live more than thirtv to forty hours even when it is 

 deposited in water, but must be again taken up by man. 



No other host except man has been found to carry on the infection. 

 How he becomes infected has not yet been proved. 



The infection is by ingestion, also probably they enter the skin 

 while people are Avorking in the mud fields or bathing in the muddy 

 pools infected by the urine of diseased persons. 



The eggs may work their way to the rectal veins and mucous 

 membrane, and then be passed out in the fseces. 



