ECHINOCOCCUS GRANULOSUS 



617 



and bores its way into the liver or some other organ. Here it grows, and 

 forms a cyst with a thick outer cuticle, inside which is fluid enclosed by a layer 

 of parenchyma, the endocyst, composed of two layers of cells. The irritation 

 caused by the growth of this cyst produces a connective-tissue coat, formed 

 by the organ in which the cyst is growing. The cyst in this condition is called 

 an acephalocyst [Echinococcus cysticus sterilis), and is often found in cattle. 



The next stage is the formation of the brood capsule. The inner layer .of 

 the endocyst grows inwards, forming large numbers of small hollow capsules 

 (brood capsules), which have the endocyst externally and the cuticle internally. 

 On these capsules heads develop. The cyst now forms the Echinococcus 

 cysticus fertilis, found in domestic animals. 



In man, however, daughter-cysts appear between the strata of the cuticle, 

 into which cells belonging to the endocyst have found their way and formed 

 cysts, with an external cuticular and an internal parenchymal layer. These 

 cysts may, of course, bulge, and escape externally or internally. If exter- 

 nally, they then lie between the capsule and the mother-cyst and form Echino- 

 coccus hydatidosus var. exogenus, or if internally, they fall into the interior of the 

 mother-cyst and form Echinococcus hydatidosus var. endogenus. These 

 daughter-cysts may remain sterile or produce brood capsules and heads. 

 Granddaughter-cysts may be formed in the same way. The wall of the 

 mother-cyst may disappear, leaving the daughter-cysts free. 



Of all these varieties, the endogenous cyst is the most common. It may 

 reach several pounds in weight, with hundreds of daughter-cysts. 



In Khartoum cysts fed into dog developed in fourteen days into worms, 

 but not quite sexually mature. 



It is believed that the usual cycle of life-history takes place in the dog and 

 the sheep. Manson suspects the jackal in India as a spreader of the disease 

 to man. Stirling and Verco lay down the following factors as necessary for 

 the spread of the disease : — • 



1. Sufficiency of infected dogs. 



2. Domestic her bivora, especially sheep, as intermediary hosts. 



3. Conditions favourable for the transmission of the parasite from the dog 

 to man. 



4. Facility of access to dogs of infected carcasses. 



Perhaps, however, the egg gains access to the human body through con- 

 taminated food and dust. 



Pathogenicity,— The cysts grow but slowly, consequently organs adapt 

 . themselves to the pressure, so that the symptoms may be wanting and depend 

 entirely upon whether the organ can or cannot expand. 



If, however, fluid escapes from a cyst, urticarial eruptions, or even rigors, 

 with local pain and tenderness, may result. 



Prophylaxis. — Prophylaxis must be on the lines indicated by the factors 

 above mentioned — viz., registration of dogs, destruction of pariah dogs, non- 

 feeding of dogs with raw meat, clean kennels, non-handling of dogs. 



Echinococcus multilocularis Leuckart, 1863. 

 Synonym, — Echinococcus osteoklastev Huber, 1896. 



This is the parasite which causes the alveolar or multilocular form of 

 hydatid disease, which is very different from the ordinary form. The disease 

 was first observed by Ruysch in 1721, and was generally looked upon as a 

 colloid cancer, until Virchow in 1856 showed that it had its origin in a worm. 

 Mangold and Muller consider that by feeding experiments they obtained from 

 it a TcBnia different from E. granulosus in the hooks and the distribution of 

 the ova. 



Melnikow-Raswedenkow gives quite a different life-history for this parasite, 

 which, if correct, will make it a new species. Further, there is the support of 

 Stiles, Stirling, Verco, and others for the differentiation of the parasites from 

 one another. 



This form of hydatids occurs in man, sheep, and pigs, but principally in 

 large cattle. 



