302 



DISEASES OF THE DIGESTIVE APPARATUS. 



take up their abode by preference in the liver or in the lungs, they 

 nevertheless do not spare the heart, the spleen, the kidneys, the 

 muscular system, the œsophagus, the reticulum, the omentum, 

 the subserous connective tissue, the eye, the brain, the muscles or 

 even the bones. 



Echinococcus is quite prevalent. According to Bollinge<r, in 

 southern Germany it is the most common infectious disease in the 

 ruminants, after tuberculosis and distomiasis. Schmidt estimates 

 that it causes a yearly loss of about 200,000 francs. Its distribu- 

 tion corresponds with that of the dog. In India, where dogs are 

 very numerous, 70 per cent, of the cattle carry the echinococcus. 



Natural history. The echinococci or hydatids are developed 

 after the ingestion of the eggs of the taenia mixed with the food or 

 with drinking-water, etc. The vesicle may be seen under the four 

 following forms : 1. Common fertile echinococcus, consisting of a 

 capsule filled with a watery liquid and containing a more or less 

 large number of heads enclosed in the proligerous cysts ; this is the 

 most frequent. 2. Compound echinococcus, formed by a mother 

 cyst containing daughter cysts (secondary), or even tertiary cysts, 

 developed either inside (endogens), or outside (exogens) of the 

 mother cyst. This form is also relatively quite frequent. 3. 

 Multilocular echinococcus. These are objectively similar neofor- 

 mations to cancer or to an agglomeration of tubercles ; on section 

 they show lacunar spaces ; they seem to be produced by the exag- 

 gerated development of an echinococcus deprived of a capsule, 

 having perforated this membrane. They are found in the he- 

 patic canals ; sometimes they acquire the hardness of stone. This 

 form is very rare. 4. Acephalocyst, which is but a headless vesi- 

 cle, and is consequently sterile. This later form is quite common. 



The embryo reach the liver through the biliary canals or through 

 the portal vein. Their development is slow : after four weeks the 

 vesicle is 1 millimetre in length; in two mouths it is 1.5 milli- 

 metre ; toward the fifth month it reaches the size of a nut. The 

 wall of the vesicle is of a gelatinous consistence, and is composed 

 of a double membrane — an external cuticle, which is very thick 

 and of lamellar structure (Jiydatic membrane) and an internal rela- 

 tively thin [parenchyma or germinal membrane). This vesicle is 

 enclosed in a cyst which belongs directly to the host, and is shown 

 to be formed of connective tissue, of thin muscular fibre and vessels; 

 its dimensions vary from the size of a pea to that of a man's head; 



