Louping-Ill in Sheep. 
555 
accompanied by a very laborious and quick respiration. The hurried 
breathing, however, subsides altogether as soon »s the tit has terminate d. 
In this state the animal will remain tor hours or days, and if he does not 
rally from it death, sooner or later, ensues. . . . Some lew instances, how- 
ever, have occurred among my Hock when they have most unexpectedly 
recovered, so as to again follow their neighbours and get entirely well, 
and in other cases they have for a length of time dragged a seemingly 
powerless hind leg behind them, and the left leg oftener than the right 
one. When this, however, takes place, the limb still remains cold and 
dead for a time in despite of the use of friction or stimulants. If it is 
a fore-leg it is not uncommon, after the sheep gets on its feet again, for 
a tumour of the size of a pigeon’s, or even of a hen’s egg, filled with 
pus or ichor, to appear. On being punctured it presently subsides and is 
lost. These abscesses usually appear in the neighbourhood of the joints ; 
but sometimes about the arms, the brisket, or any' neighbouring part of the 
body. Other symptoms of this disease are a wild excited appearance on 
being approached by a man, dog, or any other animal, and even by one of 
their own species ; a champing or gnashing of the teeth, and foaming at the 
mouth while yet on their legs, accompanied by vertigo and delirium, also 
the assuming of a rotatory or sidelong motion. . . . In this complaint there 
is also not unfrequently, when they have taken the ground, a great 
appearance of sickness. The animal likewise exhibits great restlessness 
and anxiety, mingled with debility — he trembles and tosses his limb3 about, 
as if enduring great pain. At this time there is also less of involuntary 
tremor and convulsive twitchings than at other stages of the disease ; and 
it seems as if the seat of the complaint was in the thoracic or abdominal 
viscera. ... In fact, the disease does occasionally assume so many' different 
forms, although each is more or less connected and allied with the other, 
that the most skilled veterinary practitioners may for a while be puzzled to 
say whether it is most akin to tetanus, apoplexy, or palsy.” 
At the present day no one with any pathological knowledge can 
read the last sentence quoted without a suspicion that Fair described 
not one but several different morbid conditions, for the history of 
veterinary pathology’ warns the student to be on his guard whenever 
he reads that a disease whose cause is not certainly known assumes 
many different forms. This tendency to describe diseases as assuming 
many different forms has been a fruitful source of error, and the 
reason is obvious. While the pathology of a disease — that is, its 
real nature and cause — is still unknown, its definition must rest 
mainly on a description of its symptoms and lesions, and in such a 
case it is quite unwarrantable to regard entirely different sets of 
symptoms and lesions as manifestations of the same disease. For 
example, when Fair wrote that louping-ill occasionally assumes 
many different forms he made an assumption not warranted by his 
knowledge, and he would no doubt have been puzzled to say why he 
preferred to believe that the many different forms were varying 
manifestations of one disease rather than so many different diseases. 
At the present day, both in England and in Scotland, shepherds 
appear, like Fair, to regard louping-ill as a disease that assumes 
many different forms, for during the month of April and May they 
call every case of illness in the flock louping-ill when the subject of 
it is found paralysed or unable to stand, and this quite independent 
