HERNIA OR RUPTURE 315 



through the medium of food and water. The dog having discharged with 

 his excrement the segments of the tape - worm, charged with eggs, the 

 latter will sooner or later be set free and become accessible to horses and 

 other animals in their food or water. Deposited on pasture land the ova 

 of the parasite would be taken up in grazing, and, having reached the 

 intestine of the ecpiine host, would then hatch out. 



It is believed that at this point the embryo enters the liver by way 

 of the biliary duct, and, having taken up its position in the structure of 

 the gland, proceeds to develop a cyst (fig. 113), or, as it is sometimes 

 called, a bladder-worm. After a period of five months it is said to 

 reach the size of a walnut, and may still continue to increase until it 

 becomes as large as an orange. 



Water forms the chief contents of the cysts, but from the internal 

 surface new broods of embryo tape-worms are being formed which, should 

 they escape and reach the intestines of the dog, will there mature into 

 the tape-worm Tcenia echinococcus, from the eggs of which the cysts were 

 originally derived. 



One or two, or even more, of these bladder-worms may exist in the 

 substance of the liver without in any way upsetting the balance of health, 

 but where large numbers crowd the organ and forcibly compress the 

 blood-vessels, much of the gland structure is broken up and its functions 

 correspondingly impaired. In the former case the hydatids perish, and 

 become resolved into small pasty or mortar-like masses. In the latter 

 they enfeeble and slowly destroy their host, when many of those which 

 survive, if consumed by the dog, will develop into tape-worms. 



The symptoms occasioned by these parasites are such as are met with 

 when the liver becomes infested with flukes, and seldom afford any clue 

 to the precise cause of the disease. For a long time they may but faintly 

 indicate the organ attacked. The measures of treatment therefore recom- 

 mended in the one case may also be followed in the other. 



HERNIA OR RUPTURE 



Definition. — Hernia is the protrusion of an organ, or part of an 

 organ, from its proper cavity, whether as the result of a rent in the 

 tissues, as when the belly is broken, or an escape through a natural or 

 imperfectly-closed orifice, as in inguinal and umbilical hernia. 



It is convenient to divide ruptures into two classes, viz., congenital 

 and acquired: in the one the defect is present at the time of birth; in 

 the other it is brought about afterwards, by accident or disease. The 

 causes of this latter form of the malady are severe straining, as in heavy 



