i8o 



THE ANIMAL PARASITES OF MAN 



trated into the venous plexus of the pelvis, and which eggs reach the walls 

 of the bladder, &c., from the blood-vessels. The eggs pass through the 

 walls of the bladder, and are consequently easily found in the urine of the 

 patients, mostly in the flakes. Many of the eggs, particularly those provided 

 with a lateral spine, remain stationary in the bladder, irritating it still 

 further ; but they finally perish and become calcified, the eggs remaining in 

 the lumen of the bladder are thus frequently the cause of the bladder 

 stones that are so common in bilharziosis. The eggs are also swept into 

 other parts of the body by the circulation, and may thus be found in all 

 the organs, though usually only in small numbers. 



The means by which infection is brought about are still 

 uncertain ; we only know that the mira- 

 cidia (fig. 113) enclosed in the evacuated eggs 

 do not hatch if the eggs remain in the urine ; 

 they perish with the calcified ova. As soon, 

 however, as the urine is diluted with water 

 the shell splits open, generally bursting length- 

 ways, and releases the miracidium from its 

 investing membrane, so that it can swim about 

 with the aid of its cilia. In its structure it 

 differs but little from the miracidium of the 

 liver fluke, as, for instance, in the lack of 

 eyes ; the two large gland cells situated near 

 the intestinal sac are also present in the mi- 

 racidia of the liver fluke. 



.The circumstance that this stage of de- 

 velopment already carries within it the 



bium, Bilh., with mi- germs of the future generation, indicates that 



racidium. which has , .,, . ., 



turned its anterior end sporocysts and within these cercana must 

 towards the posterior ensue ; hitherto, however, in spite of all experi- 



6f the egg. 275/1. i^i.'- ' '' v -ill j- 



(After Looss.) ments, it has been impossible to discover the 



suitable intermediary host, so that the conjec- 

 ture may be mooted that the sporocyst stage is gone through in 

 man himself. The experiments on monkeys, however, conducted 

 by Looss to demonstrate this had negative results. The infection 

 is said to be induced by drinking impure water from canals and 

 pits, and recently it has been stated that the miracidia penetrate 

 through the skin of human beings while they are bathing. 



LITERATURE 



BILHARZ, TH. Beitr. z. Helm. hum. (Z. f. w. Zool., 1852, ii., pp. 453 and 454.) 

 CHATIN, J. Obs. sur le dev. et 1'org. du proscol. de fa Bilharzia. (Ann. Sc. Nat. 



Zool , 1 88 1 [6], xi.) 

 SONSINO, P. Ric. s. sviluppo d. Bilh. (Giorn. R. Ace. Med., Torino, 1889, xxxii., 



p. 380.) 



