PARASITES OP ANIMALS. 81 



extract is generally more effectual, however. The patient 

 should have a sparing diet of soup, etc., for twelve or fifteen 

 hours before taking the medicine, and the second dose should 

 be followed, after an hour or two, by a purgative like castor- 

 oil. These remedies are mentioned here not to encourage 

 self-treatment, but for the benefit of those who may not be 

 within reach of a reliable physician. 



The margined Tape-worm of the Dog (Tcenia marginata 

 Batsch) ; and its young, the " diving bladder-worm " of 

 Sheep and Cattle. 



The young of this parasite are very frequently found in the 

 abdominal cavity of sheep, either attached to various parts of 

 the viscera, especially the liver and mesentery, or else nearly 

 or quite free among the organs, so that when the sheep are 

 opened, the bladder-like sacs fall out, of their own accord. 

 These are usually known to butchers as " water-bladders." 

 When attached to the organs, these bladders or sacs are usu- 

 ally enclosed in a cyst or membrane, formed by the inflamma- 

 tory action that they cause. The sac is soft and whitish, en- 

 closing a watery fluid, and varies in size from that of a pig- 

 eon's egg, or less, to that of a child's head ; but it is rather un- 

 common to find them larger than a hen's egg. In form they 

 are often globular, but more frequently pear-shaped, as repre- 

 sented in Figure 60. If one of these bladders, while still en- 

 closed in its cyst, be placed in a plate of warm water and care- 

 fully examined in a good light, there may be dimly seen in the 

 interior, near the upper end, the outlines of the head and neck, 

 which are turned inward, as usual in most young tape-worms ; 

 but what is singular in this case, the head and neck alternately 

 rise and sink in the fluid of the interior, with remarkable reg- 

 ularity. From this peculiarity it lias received the name of 

 " diving blacbder-worm." This motion is produced by a pe- 

 culiar arrangement of muscular fibres in the interior, which 

 are attached to the neck. At the top of the little knob on the 

 upper end of the bladder there is a small slit, from which, by 

 gentle pressure, the neck may be gradually forced out, so as 

 to project externally, and finally the head also appears. In 

 11 



