34 



The Rot in Sheep. 



structural changes lead to a partial blanching of the lobules, and 

 a greatly impaired function of the bile-secreting cells, so that at 

 length the entire organ becomes of a yellowish or clay-like hue, 

 with which the enlarged main-biliary ducts greatly contrast, 

 standing" out on its surface as bluish-white lines or bands. 

 Much more might be added with reference to these pathological 

 changes, but our description of the post-mortem appearances must 

 not be anticipated. 



Anatomy and Natural History of the Liver-Fluke. 



The branch of science commonly designated Natural History 

 is acknowledged to be far more attractive than many others, and 

 to possess allurements even for the uneducated. If this be so, 

 it is easy to understand how men whose education and tastes fit 

 them for such a study often become enthusiasts in its pursuit. 

 It is well when investigations of this kind are not undertaken 

 for mere intellectual gratification, but have for their end some 

 praiseworthy object — the benefit, perchance, of the human race. 

 It is this which gives a value, far beyond the simple attainment 

 of knowledge, to researches into the history of parasites, because 

 they mostly lead to the means of cure or prevention of the 

 diseases which are due to the presence of these creatures. The 

 introduction of the achromatic microscope has immensely in- 

 creased the facilities for obtaining precise information on this 

 subject, and has consequently led to the dispersion of many 

 an error which formerly prevailed. A new field of research 

 has thus been opened up, and the facts already revealed make 

 even the profoundest naturalist hesitate in expressing an 

 opinion on the development of parasites which he himself has 

 not investigated. 



Only a few years have elapsed since the scientific world was 

 startled by the announcement of Von Siebold that the hydatid 

 of the brain of the sheep, the cosnurus cerebralis — the cause of 

 the disease termed " gid " — was only the scolex of the Tcenia 

 serrata of the dog, and that the detached segments of this worm, 

 in which its ova were perfected, would, if given to sheep, 

 produce hydatids in the brain. Nor was this the only proof 

 adduced in corroboration of the statement, for it was said that 

 the converse was equally true — namely, that tape-worms were 

 quickly developed in the intestines of the dog, by giving to this 

 animal the so-called heads of the cosnurus. 



A number of experimentalists was thus called forth, on the 

 the Continent in the first instance, and afterwards in England, 

 every one of whom confirmed the conclusions arrived at by 

 Siebold. It was proved beyond disputation that some, at 



