274 THE ANIMAL PARASITES OF MAN 



of the submucosa in the bladder, and the eggs in the mucosa, and 

 those voided are usually terminal-spined, though lateral-spined eggs 

 are not so rare as generally thought. The problem next arises as to 

 how the eggs get to the lumen of the gut or bladder. 



The female worm is 280 //, in diameter. Veins in the submucosa 

 of the rectum less than 178/1, in diameter are not affected with endo- 

 phlebitis. It is probable that the female even by stretching could not 

 penetrate much beyond this. Eggs are probably then laid in the 

 submucosa as near the muscularis mucosa as possible. Now if the 

 eggs are laid in a vein of larger calibre than the worm fills, the eggs 

 would be carried back to the inferior mesenteric vein, so that pre- 

 sumably the worm must succeed in blocking the vein already narrowed 

 by endophlebitis, so that by the stasis which ensues the eggs may 

 escape from the veins. How this occurs is not exactly known ; it is 

 not necessarily due to the spine, as the same escape into the tissues 

 occurs in spineless eggs, such as those of Schistosoma japonicum. The 

 eggs, then, pass as foreign bodies through the tissues. Another hypo- 

 thesis is that the worms leave the veins in order to lay their eggs, 

 but the evidence is against this. 



Caval System. Occasionally worms that have passed through the 

 vesical plexus may be found in the iliac vein, inferior vena cava, 

 and even the lungs. If the worms are young they contain a lateral- 

 spined egg ; if adult, numerous (50 to 100) terminal-spined eggs. 



Lungs. When the liver is strongly infected with (terminal-spined) 

 eggs it is possible that by passive movements some may pass into the 

 intralobular veins, and thence by the inferior vena cava to the lungs. 



Gall-bladder. Similarly terminal-spined eggs pass into the bile- 

 capillaries and gall-bladder (where they may be abundant), and so into 

 the faeces. 



Detection of Eggs. Occasionally eggs may be found in various other 

 parts of the body. They are best detected by macerating pieces of the 

 tissue in question in about \ per cent, hydrochloric acid at 50 to 60 C. 

 (Looss). 



Pathological changes : 



Rectum. These have been studied thoroughly by Letulle in the 

 case of an apparently pure infection of the rectum. 1 They take the 

 form of a chronic diffuse inflammation, which may result in (i) ulcera- 

 tion, or (2) hyperplasia of the mucosa, producing adenomata. 



Ulcerative Form. The mucosa is transformed into a mass of 

 vascular connective tissue. The connective tissue spaces next be- 

 come invaded by numerous mononuclear cells. The tissue itself 



1 It is noteworthy that in this almost classical case no worms were found in any of the 

 sections. It is further noteworthy that the eggs in the rectum showed great irregularity of 

 form. Eggs with a spine at each end were not uncommon ; exceptionally eggs with two 

 polar spines and one lateral. 



