472 
CHARLES COWIE. 
Before eonsideriiig the causes of thoroughpin let us glance 
for a inoinent at the structure and uses of a bursa in health. It 
is a thin membrane lining joint cavities and sheaths of tendons, 
secreting an oily fluid called synovia, to prevent undue friction 
between structures that move on each other. It is similar to 
the serous membranes that line the thoracic and abdominal 
cavities, made up of pavement and endothelian cells and under¬ 
neath are more or less dense fibrous stroma, containing nerves 
and blood-vessels. The fluid secreted is of a pale yellow color 
of an oily consistence. A bursa in normal condition is found to 
contain only a sufficient quantity to lubricate its interior, but 
in disease may accumulate such a quantity as to assume large 
proportions. 
In regard to causes : when we consider the almost complete 
immunity from bursal distention found in other animals, we are 
led to the conclusion that it is the nature of his work ; and when 
an animal presents bursal distention, we consider that he has 
been worked or driven prematurely. 
Over-driving, over-working, sprains or other injuries, slip¬ 
ping on pavements or otherwise, will often produce thorough- 
pin. 
With some horses there is a predisposition from an inherited 
weakness, either local or systemic. 
In regard to the pathology : in its first and simplest form it 
consists of a simple distention of the bursa, with a superfluous 
quantity of its normal secretion, without any inflammatory ac¬ 
tion, causing neither pain nor lameness, and due to an increased 
activity of the cells, the synovia being secreted faster than it 
can be absorbed or used. In some cases, however, especially 
when the direct result of a severe sprain, inflammation and 
lameness are prominent symptoms. In some cases, as time goes 
on, the bursal walls become thickened and hardened. The con¬ 
tain fluid altered in consistence ; and in the case of wind-galls, 
has been known to become osseous. In most cases there is no 
structural alteration whatever, and when once formed persist¬ 
ently remains so. 
