126 
TIic Rot in Sheej). 
only a slight impairment of function, due to a hidden or unknown 
cause of irritation, are of all others the most difficult to diagnose. 
Among these may be named some of the parasitic maladies, 
of which rot in sheep may be taken as an example. Even in 
those instances where no difficulty exists with regard to the time 
of the application of the cause of rot, we sometimes look in 
vain, for many weeks, for clear evidence of its existence. 
Simon, in his ' Lectures on General Pathology,^ delivered at St. 
Thomas's Hospital, in the session of 1850, rightly remarks that 
"if you examine parasitic diseases from first to last, you will 
find that they are, perhaps of all known maladies, the most essen- 
tially local. They may be very extensively diffused — may be in 
very many spots of the body — and the sum total of many small 
irritations may be a large general irritation ; or if the parasites 
are large, as well as numerous, they may drain the system of 
blood, and ana^miate and kill the animal, as we see in the rot of 
sheep. But all we know of parasitic influence on the health — 
and I may observe that a good deal is known — all, I say, is 
referable to these two heads : local inconvenience from pressure 
or from irritation ; (jeneral inconvenience, either febricular, from 
that local irritation becoming inflammatory, or anaemiative by 
draining and impoverishment of the blood." 
The latent stage of rot — viz. the period which elapses between 
the entrance of the penultimate forms of the fluke and their 
change into perfect flukes and attainment of sufficient size to 
begin to drain the organism — is the one which perhaps interests 
the pathologist more than any other. He sees in it the gradual 
development of causes which he would fain interpose to arrest : 
because, if unchecked, he knows they must ultimately undermine 
the constitution. But he is without sufficient warrant to take 
action, in so far as the animal itself is concerned, for he can recog- 
nise no symptoms of ill health. In some instances, however, prac- 
tical knowledge will come to his assistance, and when he finds 
animals surrounded by circumstances that experience has proved 
will engender rot, he does not hesitate to put into operation the 
power of prophylactics. 
The latent stage of the disease is also the one of the first 
importance to the practical agriculturist. During its continuance 
he may avail himself of many means which will to a great 
extent secure himself against loss ; but he, also, too often fails in 
the right application of these, because he is not warned by any 
symptoms to suspect the existence of the malady. 
Much has been said about sheep fattening somewhat quicker 
than is usual in the early stages of rot, and occasionally attention 
has been draAvn to this circumstance as warranting a suspicion 
of the animal's soundness. Mr. Youatt, when speaking of the 
