22 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 
Symptoms and lesions—The blood strongyles injure the wall of 
the gut to which they are attached. These worms suck a tuft of 
the inner wall of the gut into their mouth cups (fig. 15) and abstract 
blood from this delicate lhning. As the worms move from one place 
to another within the gut they expose its injured wall to the entrance 
of disease-producing bacteria. Bloodworms abstract blood from the 
finer blood vessels in the lining of the gut, and when many worms 
are present in a horse at the same time the loss of blood may be 
considerable and may lead to anemia with the usual consequences 
of weakness and of watery swellings (edema) in various parts of 
the body. These worms also produce injuries of various sorts in 
the parts of the body to which they wander, such as the liver, 
pancreas, and other 
organs. 
One species, the 
single- toothed 
strongyle, is espe- 
cially injurious be- 
cause aS an imma- 
ture form it settles 
in certain arteries, 
especially in the an- 
terior mesenteric 
artery which sup- 
plies blood to the 
large gut. As a re- 
sult of the presence 
of the worms in this 
blood vessel, the 
wall of the artery, 
where the worms 
- accumulate, becomes 
thickened and 
Figure 15.—Section through the wall of the large gut, stretches consider- 
showing the head end of an attached blood strongyle, 
S. equinus, with a tuft of the inner lining of gut drawn ably to form what 
Se of the worm. Greatly enlarged. is known as an 
aneurism An 
aneurism is a spindle-shaped, cylindrical, or globular dilation of a 
blood vessel and often contains a heavy deposit of fibrin inside. In 
the horse it may attain the size of a child’s head. (Fig. 16.) 
An aneurism interferes to a considerable extent with the circula- 
tion of blood through the affected artery, because the heavy deposits 
of fibrin inside may almost obliterate the lumen of the blood vessel. 
This condition results in a diminished blood supply to the large 
intestine; when the intestine becomes anemic as a result of this it 
becomes predisposed to colic, twist, and intussusception, the last 
being a condition in which part of the gut slips into an adjoining 
part. When a piece of fibrin deposit in “the aneurism breaks loose, 
it may be carried in the circulation to a terminal portion of an artery 
and may lodge there as a plug. As a consequence, the circulation 
to a part of the large gut may be completely shut off. Such a con- 
dition interferes with the functions of the large gut, produces an 
anemic condition with the consequences noted above, and in extreme 
