Etiology. 469 



According to Melnikow the cysticercus of this Tienia (Cryptocystis trichodectis) 

 is found in the hair parasite of the dog, Trichodectes latus canis, and according to 

 the more recent investigations of Grassi in the dog flea Pulex serraticeps, also in 

 the flea of man, Pulex irritans. Dogs infect themselves by ingesting these parasites; 

 even sucking puppies may do so (parasites 2.5 cm. long were found in a puppy 10 

 days old, and mature Teenia in puppies 1 to 2 months old). 



5. Taenia echinococcus. Three or four segments, not over 5 mm. long. 

 Scolex provided with four suckers and a rostellum of 28 to 50 small hooks, arranged 

 in two rows. The second and third segments are incompletely developed and the 

 fourth only is sexually mature. The embryo remains alive in the ovum when desic- 

 cated for 10 or 11 days, in water 10 to 16 days. 



This Taenia develops from Echinococcus polymorphus found in the internal 

 organs, preferably the liver and the lungs of ruminants, hogs, also of man. After 

 the ingestion of such infected organs by dogs there develop usually numerous Tienia 

 in the intestines of these animals, since every bladder ordinarily contains several 

 hundred protoscolices. Tamia develop from these in 6 or 7 weeks. Different species 

 of Taenia echinococcus are developed from Echinococcus cysticus and E. alveolaris, 

 according to claims of Ostertag, Midler, Mangold, and Possell. 



Much rarer than those enumerated are Taenia lineata, T. serialis, T. Krabbei. 



In regions where dogs have occasion to eat fish they also 

 harbor Bothriocephalus (seen in Hungary by v. Ratz). The ova 

 of this intestinal parasite set embryos free in water, which are 

 supplied with cilia that wander into fishes (perch, pike, lake 

 trout, brook trout) to infect their intestinal muscularis or other 

 organs as band-shaped pleurocercoids. If taken up with the 

 infected fish they soon develop in the intestinal tract of dogs 

 and form mature segments after four weeks. Bothri- 

 ocephalidae are flat, the head is elongated with two longitudinal 

 furrows, the surface of the mature segments shows 

 the rosette- shaped uterus which open up on the 

 surface. 



The most common representative is Bothriocephalus latus 

 which is found particularly on the shores of large bodies of water, 

 also in man. This worm is 2 to 7 meters long in dogs; the head 

 is lancet shaped, the mature segments are 4 to 6 mm. long and up 

 to 2 cm. wide. After the ova have been deposited the segments shrink Fig- 54. Ovum 

 (mature segments are not detached like those of Tajnia). Ova of bothrioceph- 

 oval OS to 71 /x long, 44 to 45 /x wide ; they have a lid at one pole alus latus. 



which can be well seen after treatment with sulphuric acid (fig. 54). 



Other Bothriocephalidae are found in Iceland and Greenland (b. curdatus, b. 

 fuscus). 



Concerning the occurrence of various Taenia in dogs, the 

 following may be said : 



Dipylidium caninum is found most frequently, because dogs 

 infect themselves easily ])y the fleas and lice found in their coat. 

 Butchers' dogs infect themselves easily with Tsenia echinococ- 

 cus, T. marginata and T. cojnurus; shepherds' dogs particularly 

 with T. coenurus ; hunting dogs with T. serrata. The frequency 

 of the occurrence of these tsenias also depends, a good deal, 

 upon external circumstances. Tapeworms in dogs are rarer in 

 large cities with well regulated slaughter houses, with strict 

 meat inspection, and more common in the country where the 

 supervision is less rigid. Young dogs are more susceptible to 

 infection than older animals. 



There may be several species of Taenia in one host. The 



