THE EXPERIMENTS OF KNOCK. 



717 



helminthologists (Linne, Pallas, and Krabbe) infected by them in all 

 localities where the parasite abundantly occurs. 



It is now unnecessary to criticise in detail 1 these statements 

 maintained by Knoch with so much confidence, yet it is perhaps not 

 superfluous to remember that the long period of incubation, and the 

 character of the embryos, are facts which Knoch had opportunity 

 enough to observe, and are of themselves enough to cast doubt upon 

 his results, nor have I, though sufficiently convinced, omitted to 

 repeat Knoch's experiments. In Giessen, where there are no Bothrio- 

 cephali, I have not only experimented on dogs, both young and old, 

 with fresh ova and with ciliated embryos, but have, along with 

 several of my pupils (more than eight persons), swallowed each a 

 dozen embryos, without ever obtaining anything but a negative 

 result. 2 



Eecent progress has thoroughly justified my opposition to Knoch, 



fl 



and it has meantime been experimentally proved 



by Braun that Bothriocephalus latus has an inter- c 



mediate host, in which alone its development is 



perfected. This intermediate host is a fish, and 



especially the pike, an animal which, according to 



Braun's researches in Dorpat (long known as a home 



of Bothriocephalus), so frequently contains larval 



forms of this parasite, that among the specimens 



from the Peipus, the Wirzjaw, and the Eubach, it 



is very rarely that one is found without parasites. FlG - 377. Larvw 



rri A> i 11 i ,1 of Bothnocephalus 



The worms are found encapsuled, not only in the latus from the 

 most varied positions in the viscera, but also in the P\ k - A a , nd # 



i j n -j T_i 1. Wlth extended, O 



muscles, and usually in considerable numbers, so with contracted 



that pikes of little more than a span long some- 

 times contain in the flesh alone thirty or more. 



The pike, though the favourite, is not the only host of this worm. 

 It occurs also, according to Braun, in the burbot (Lota vulgaris), in the 

 same organs as in the pike, but less constantly and less abundantly. 

 It is possible, further, that in course of time we shall become 

 acquainted with other fish which are intermediate hosts of this 

 Bothriocephalus. 3 



1 See also my remarks published at the time (loc. cit.), and also the criticism of 

 Braun (loc. cit., pp. 6-12). 



2 Loc. cit., Th. i., p. 764 ; Th. ii,, p. 867. 



3 Thus Dr. J. Ijima, Tokio, informs me that in Japan, where Bothriocephalus is fre- 

 quent, the pike hardly ever occurs. He conjectures that the cystic form is harboured in the 

 species of salmon (Onchorhynchus Huberi and 0. Pcrryi), which are eaten not only salted 

 and fried, but in certain districts raw in sauce, like bonettas, mackerel, plaice, carp, &c. 

 Fish form an important constituent of food throughout Japan, 



