The Rot in Sheep. 
95 
gaininp; access to the parencliyinatous structure of the liver ; and 
in eflcctiiii^ tliis she does not even stop at mere membranous 
deveh)pineiit, but often deposits calcareous materials within the 
animal tissue. This gives to the liver its hardened condition, 
and likewise imparts a J^ritty sound on cutting throufjh its sub- 
stance. The same structural changes lead to a partial blanching 
of the lobules, and an impaired function of the bile-secreting 
cells, so that at length the entire organ becomes changed in 
colour, often presenting a yellowish clay-like Ime, with which 
the enlarged main-biliary ducts greatly contrast, standing out 
on its surface as bluish white lines or bands. Much more mijrht 
be said with reference to these pathological changes, but our de- 
scription of the j)ost-tno7'tem appearances must not be anticipated, 
and therefore we pass onwards to our next division, namelij, the 
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 Avhose 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 know- 
ledge, 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 increased the facilities for 
obtaining information on this subject, and has consequently led to 
the dispersion of many an error which had formerly prevailed. A 
new field of research has thus been opened up, and the wonders 
already revealed make the profoundest naturalist hesitate in 
expressing an opinion on any one point connected with the develop- 
ment of these creatures which he himself has not investisrated. 
Only a few years have elapsed since the scientific world Avas 
startled by the announcement of Von Siebold that the Cyticercus 
fasciolaris — the hydatid met with in liver of rats and mice — was 
only a "stray tape- worm which had become vesicular, and was, 
in fact, the Taenia crassicolis of the cat." Shortly after this, even 
greater surprise, amounting in some persons to unbelief, was 
produced when the same distinguished naturalist affirmed that the 
hydatid of the brain of the sheep ccejuirus 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, 
