PARASITES AND THEIR DEVELOPMENT. 



185 



FIG. 17. Liver- 

 fluke, or Fasciola, 

 magnified. 



bodies, each about three-quarters of an inch long, are found 

 within the bile-ducts ; whilst in the bile itself thousands 

 of small particles are to be discovered by microscopic aid. 

 The small flat bodies are "flukes" (Fig. 17), 

 and the particles are the eggs of these animals. 

 What, it may be asked, are these flukes, which, 

 according to trustworthy evidence, carry off 

 annually between one and two millions of 

 sheep at the very lowest computation ? The 

 reply to this question is readily given. The 

 "liver-fluke" is one of a group of internal 

 parasites which has been known from com- 

 paratively early times. It was certainly 

 known in 1547, and was lucidly described 

 in 1552 by an author who was shrewd enough 

 to attribute to its presence an epidemic which 

 decimated the flocks of Dutch farmers in that 

 year. Its "area of distribution," to use a scientific but expres- 

 sive phrase, is not confined to sheep alone, but includes cattle, 

 the horse, hares and rabbits, the spaniel, deer and antelopes, 

 and even man himself. A little flat and somewhat oval body, 

 with a tree-like arrangement of tubes for a digestive system, 

 and possessing a couple of suckers for adhesive purposes, 

 such are the main features which a liver-fluke presents for 

 examination. A more innocent-looking animal could hardly 

 be found, and the cause of its injurious effects upon its 

 animal hosts might remain a mystery, did our inquiries cease 

 with the investigation, so to speak, of its personnel. 



A highly important consideration, however, and one 

 which extends beyond the restricted domain of our present 

 subject, is that which recognises in numbers and time two 

 important factors in elevating agencies of apparently unim- 

 portant kind into forces of vast or uncontrollable nature. 

 The rain-drop is insignificant regarded merely as a particle 

 of water, no doubt but multiply your rain-drops indefinitely, 

 and you obtain the agent which will wear the hardest rock, 

 excavate the giant cavern, or form the foaming cataract with 



