356 THE ANIMAL PARASITES OF MAN 



on growing. In the distribution of this secondary echinococcus the 

 great powers of motility of the free scolices must be taken into 

 account (Sabrazes, Muratet, and Husnot). 



Human echinococci may also die at various stages of development, become 

 caseous or calcified, or may be absorbed, the cause for this being either disease of 

 the hydatid itself or inflammation of its connective tissue capsule ; the discovery of 

 the laminated cuticle, which has great powers of resistance, or the finding of the 

 hooklets of the scolices is sufficient to form a conclusion as to the nature of such 

 formations. 



Siebold (1853) was the first to rear Tcenia echinococcus in the dog 

 by feeding it with the echinococcus of cattle and especially of sheep. 

 Kuchenmeister, van Beneden, Leuckart, Railliet and others obtained 

 similar results, and Thomas, Naunyn, Krabbe and Finsen succeeded 

 in rearing T. echinococcus in dogs from the bladder worms of human 

 beings ; these grow comparatively slowly (one to three months 1 ) and 

 only during the process of growth develop their hooklets in their 

 definite form (fig. 258). It lies in the nature of things that dogs, 

 whether experimentally or naturally infected, almost always harbour 

 T. echinococcus in large quantities. That cats exceptionally harbour 

 these worms has been already mentioned (Deve). Finally, Leuckart 

 infected young pigs by feeding them with mature segments. 



Echinococcus multilocularis (alveolar colloid). 



In addition to the form of echinococcus already described, and 

 which is also frequently termed Ecliinococcus unilocularis, there is a 

 second form which occurs in man as well as in animals, and which 

 is termed E. niultilocularis, s. alreolctris (alveolar colloid). 



It was originally regarded as a tumour ; its animal nature was first 

 established by Zeller and R. Virchow. The parasite, which varies 

 in size from that of a fist to a child's head, presents a collection of 

 numerous cysts, measuring between o'i and 3 to 4 mm. to 5 mm. 

 in diameter, which are embedded at first in a soft, connective tissue 

 stroma ; the cut surface has therefore a honeycomb appearance. The 

 cysts are surrounded by a pellucid and laminated cuticle, and each 

 according to its size encloses either a small-celled tissue or a cavity 

 lined by a parenchymatous layer ; the fluid contained in such a cavity 

 may be transparent, or is rendered opaque by globules of fat, bile- 

 pigment, haematoidin and fat crystals. According to some authors 

 all or most of these cysts intercommunicate ; others state that this is 

 the case at least as regards the cuticle. The scolices are by no means 



1 According to Perroncito the scolices had not formed proglottids nine days after feeding, 

 but the latter were present twenty-four days after feeding, although the formation of eggs had 

 not begun. 



