EXAMINATION OF HELMINTHES 135 



the manner in which the two families, Opisthorchis and Dicrocoelium, 

 differ from one another. Other species belonging to these families, 

 but proceeding from other hosts, differ in several minor particulars, 

 of which space does not permit a description here. 



The liver-fluke (Fasciola hepatica) should first be examined in the 

 fresh state, living material being easily obtained from abattoirs. It 

 grows to a length of about 30 mm., and is found in the gall-ducts of 

 sheep and cattle. In infected animals, the vessel walls become thick- 

 ened and encrusted, and they are frequently dilated to such an extent 

 that the vessels stand out above the surface of the liver. To obtain 

 the flukes, the gall-ducts should be split lengthwise, when cystic 

 pouchings containing flukes will frequently be found. 



The flukes should be washed in normal saline, laid upon a large 

 glass slide and carefully stretched with the finger, as they frequently 

 contract when exposed to a temperature lower than that of the body. 

 In appearance, the fluke is a largish, tongue-shaped body, which is 

 prolonged anteriorly into a small, flattened, cone-shaped head process. 

 The difference between the dorsal and ventral aspects should be care- 

 fully noted, the ventral surface being recognized by the sucker, which 

 has a diameter of 1'5 to 1*6 mm. and is situated in the middle line at 

 the point where the head-cone widens out into the body. Close to it 

 is the genital opening, from which the long curved cirrhus frequently 

 projects. The scales, by which the anterior portion of both aspects is 

 covered and which project slightly beyond the cuticular layer, are less 

 easy of detection. They may be seen, however, if the parasite is taken 

 up on the finger and, after carefully drying with blotting paper, 

 examined with a strong glass. 



If a live fluke is pressed between two glass slides and held, either 

 up to the light or over a white background, a good deal of the internal 

 structure will be seen with a magnifying glass or low-power microscope, 

 or may even be made out with the naked eye. It frequently happens 

 that the stomach-tubes are filled, either entirely or in part, with a dark 

 brown fluid, which acts as a sort of natural injection in showing the 

 the course of the digestive organs. This fluid is blood which has under- 

 gone certain changes. The oral sucker will be found at the tip of the 

 head-cone ; behind it, in the middle line, is the pharynx, immediately 

 beyond which the oesophageal tube divides. At the level of the ventral 

 sucker, the two branches of the stomach-tube diverge somewhat, 

 though they almost immediately again approach the middle line, and 

 this position is maintained through the rest of their course. The 

 tubes in front of the ventral s acker are furnished with four to five 

 slightly forked appendages, which extend forward and towards the 

 sides. There are similar processes beyond the ventral sucker; these 

 are, however, much longer and divide up into numerous ramifications. 



