FISTULOUS WITHERS 25 
In the so-called foot rot of sheep, we have, in the cases which 
have come to our notice, conditions similar to those found in the 
cattle that were suffering from suppurative cellulitis. These cases 
are to be differentiated from necrosis of the skin above the coronary 
band due to Bacillus necrophorus. (See ‘Lip and leg’ ulceration). 
Fistulous withers and poll-evil. Recent investigations indicate 
that these very common and troublesome local diseases are either 
directly or indirectly the result of bacterial invasion. This conclu- 
sion is drawn from the fact that the bacteriological examinations 
made from the pus and from recent lesions in these affections invari- 
ably reveal the presence of streptococci or micrococci, or both. 
Gay found a streptococcus in each of seven cases of common fistulous 
withers and in two cases of poll-evil. It was invariably associated 
with a micrococcus. He found in five cases of deep seated shoulder 
abscesses M. pyogenes only. It is instructive to note, that bacteria 
closely resembling this organism have frequently been found in the 
deeper layers of the skin of the horse. The mechanical injuries 
commonly attributed as the primary cause consist usually of little 
more than skin irritation from ill fitting harnesses, saddles or from 
blows. While these are mechanically not extensive, they are suffi- 
cient to liberate into the juices of the subjacent tissues the bacteria 
deeply seated in the integument. It is not unlikely that in some 
cases the lesions are due to infection, through metastasis, from 
bacteria that gain entrance through the walls of the digestive tract. 
The inflammatory process leading to suppuration, the formation of 
fistulee, the new formation of fibrous tissue in the affected parts, 
and even the bone necrosis occasionally seen are all possible results 
of the activities of the pyogenic bacteria found in the lesions. There 
is nothing in their character to suggest causative agencies other 
than microorganisms. The tissue changes involved in the deposition 
of fibrous tissue and the abscess formation are known as the results 
of infection as well as the inflammatory processes following them. 
These affections are mentioned in this connection simply because 
the accumulating evidence tends to strengthen the working hypothe- 
sis that they are the result of bacterial invasion. 
The morbid changes in the tissues are those of acute or more 
chronic inflammation. 
Infectious mastitis. Cattle suffer frequently from an acute 
inflammation of the udder as the result apparently of an invasion by 
