FREQUENCY OF OCCUKEENCE. 637 



with him ; but this point of difference is of little consequence. In the 

 latter case, as in the former, both proglottides and eggs may in many- 

 ways be carried in food or on the hands to the mouth, and thus reach 

 the intestine ; and that the more readily, since dogs are fond of 

 licking the hands or faces of their masters, and equally fond of snuffing 

 at the anus or dung of other dogs. They may thus be in a sense inter- 

 mediate hosts, and yet themselves remain free from the adult Taenia. 



Too familiar association with dogs is, indeed, anything but safe, 

 and that especially in places and under circumstances (such as 

 sausage-manufactories and slaughter-houses) where the dogs can 

 readily obtain portions of ^cAzwococCTts-bladders, and develop them 

 into sexually mature tape-worms. "VVe must prevent dogs from 

 licking us, banish them from room and kitchen, keep them clean, and 

 see that their excrement is as far as possible removed. Further 

 suitable precautions should be taken to prevent an infection with 

 embryos of Ecliinococcus ; the dogs should be kept away from places 

 where the bladders are thrown carelessly away, or even given to 

 dogs as tit-bits. The careless disposal of these "water-bladders," 

 and the unnecessarily large number of dogs, have most to do in 

 perpetuating and propagating one of the most severe and dangerous 

 forms of helminthiasis. 



From the universal distribution of the dog, as well as of herbi- 

 vorous domestic animals, that is to say, of those creatures which mainly 

 facilitate and provide for the cyclic development of Tcenia ecliinococcus, 

 it is easy to suppose that the cystic worm is everywhere developed in 

 man. Experience has completely established the accuracy of this 

 conclusion, for we now know not only of cases of Echinococcus from all 

 parts of the world, but are also acquainted with the fact that in some 

 countries the disease is endemic, and endangers the health and life of 

 the inhabitants more than any other illness. 



Among these countries is Iceland, where the Echinococcus disease 

 (the so-called " liver plague ") is so frequent that the Danish govern- 

 ment was compelled to send thither a special expert to investigate 

 its causes, and check its further spread by suitable arrangements. 

 Although indigenous there for centuries, the parasitic nature of the 

 disease was only discovered about thirty years ago, indeed, by Schleis- 

 ner,i who spent two years in the island for medical purposes. On the 

 ground of his own investigations and of the testimonies of the local 

 physicians, he estimated the number of patients suffering from hydatids 

 at one-sixth to one-eighth of the whole population, that is to say, 10 to 

 15 per cent., or altogether about 10,000 persons. Although Thorstensen, 

 who practised in Iceland for more than twenty years, also believes that 

 ' " Island, undersogt fra et leegevidenskab. Synspunkt :" Kjobenhavn, 1849. 



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