CESTOID INTESTINAL WORMS. 71' 



the Vistula, and that it is rare, whilst the taenia is 

 comparatively common, in the districts situated upon 

 the western side of that river. Some writers. Yon 

 Siebold amongst the number, go so far as to look 

 upon the Vistula as a complete line of demarcation 

 between the two genera, in the countries which con- 

 stitute Western Europe. 



Owing to the circumstance that the countries in 

 which the bothriocephalus is endemic border upon 

 the sea, lakes, or rivers, the cause of the existence 

 and of the frequency of this worm has been naturally 

 sought for in some condition which is common to 

 these various countries. 



It was for a long period supposed to depend upon 

 the fish diet which is largely used by the inhabitants 

 of these locahties, but arguments, chiefly founded 

 upon the limitations of the appearance of the bothrio- 

 cephalus to certain districts, and to its total absence 

 in others, where a fish diet is also much employed, 

 have not been wanting to invalidate tliis view ; and 

 it is highly probable that if this be one of the causes, 

 there are others of a local character which are equally 

 active. 



The existence of the bothriocephalus in particular 

 countries which bear an evident analogy to each 

 other, and that of taenia in countries of a most 

 dissimilar nature, — situated at the sea- coast as well 

 as in the centre of continents, in arid deserts, under 

 all latitudes, and at various heights, — shows a marked 

 distiQction in the mode of propagation of these two 

 cestoid worms. 



There are good reasons for the belief that the 

 transmission and propagation of the taenia solium 



