Infecting mice with S. japonicum cercariae from snails mashed on the abdominal surface of the mouse, it was found by Suyeyasu that after penetrating the skin the cercariae went to the right heart by way of venous and lymphatic channels. From the pulmonary vessels they penetrate the lungs and go by way of the mediastinum or pleura to the diaphragm which they penetrate and make their way to the abdominal cavity next penetrating the liver and entering the portal vein.
It is probable that the earlier stages of development take place in the portal vein and that having reached maturity the female attaches herself to the male and together they go, by way of the inferior mesenteric vein, to the haemorrhoidal or vesical terminals. The male is in the shape of a narrow leaf, about ½ inch long with a ventrally turned oral sucker and a closely adjacent ventral sucker. The female is a somewhat longer and cylindrical worm almost an inch in length and, like the male, has two suckers. There is a dark brown zig-zag stripe which shows prominently in the posterior part of the female and outlines the blood-filled intestinal tract. When the female applies herself to the ventral surface of the male there is an infolding of the sides of the flattened surface giving the male a cylindrical outline and resulting in the formation of a canal containing the female (gynaecophoric canal).
Fig. 106.—Schistosoma japonicum (male and female). The sharp edges of the borders at the beginning of the gynaecophoric canal formed by the male are an accidental appearance. (From Mense.)
The males of the flukes which cause the vesical (Schistosoma haematobium) and the rectal (Schistosoma mansoni) involvement are covered externally with small tubercles and have a ventral sucker only slightly larger than the oral one. The Japanese schistosome (Schistosoma japonicum) is slightly smaller, has a smooth surface and shows a prominent pedunculated ventral sucker of much larger size than the oral one.
Both suckers are larger than those of the other species.
The eggs of S. haematobium have a terminal spine and measure from 115 to 175 by 60 microns; those of S. mansoni have a lateral spine and measure from 110 to 125 by 50 microns while those of S. japonicum are devoid of spinous projections and measure about 100 by 70 microns.
Clinically, the three infections differ as will be noted further on.
Looss claims that the two tuberculated species are identical and that the lateral spined egg is the product of an unfertilized female. He has more recently regarded the egg as produced parthenogenetically. Other helminthologists have noted slight anatomical differences as to ovaries and testicles so that the consensus of opinion is that vesical and rectal bilharziases are caused by different species of the genus Schistosoma.
