26 INFECTIOUS MASTITIS 
a number of bacteria. The results of the investigations of this 
affection thus far reported suggest that the form which is transmitted 
from animal to animal is caused by a streptococcus. It is, however, 
impossible without a bacteriological examination to distinguish 
between this affection and those caused by other bacteria. It seems 
likely that many cases are primarily brought about by mechanical 
injuries which render possible the entrance into the fresh tissues of 
the bacteria of the skin or of the milk ducts. Other cases may be 
due to infection through the teat of bacteria capable of producing, 
by means of their metabolic products, the inflammatory condition 
without a distinct injury to the mucous membrane. The former 
view that there ‘was a sphincter muscle near the base of the teat 
which closed the duct sufficiently to prevent the entrance of bacteria 
to the secreting portions of the gland was not founded on anatomical 
facts. 
The inflammatory affections of the udder fall very naturally 
into two general groups, namely: (1) those in which the parenchyma 
is most affected and (2) those in which the stroma or fibrous tissue 
is involved. In many chronic inflammations they are both included. 
The form of mastitis more frequently encountered as an infectious 
(transmissible) disease is characterized by very marked changes in 
the milk, accompanied by the usual symptoms of parenchymatous 
inflammation of the gland itself. The discharge from the affected 
part of the udder usually contains flaky masses held in suspension 
in the clear or perhaps cloudy serum. The color varies, and occa- 
sionally the fluid is blood-stained. The microscopic examination 
shows the presence of agglutinated fat globules, pus cells and often 
red blood corpuscles. 
A number of bacteria* considered of more or less etiological value 
have been associated with lesions of doubtful origin. The results 
of Kitt, Nocard, Mollereau, Guillebeau, %schokke, Bang and still 
others, in which a Bacterium, a Bacillus, a Micrococcus, a Staphylococ- 
cus, and a Streptococcus have been found and reported as standing 
in a causal relation to the trouble, indicate that a variety of micro- 
Organisms are active in producing those affections which are fre- 
quently grouped without distinction as infectious mastitis. The 
*Among the bacteria which have been found in udder trouble and described as 
a possible or perhaps the more probable cause the following species may be mentioned: 
Bactertum phlegmasie uberis, Streptococcus agalactise. contagiosa, Staphylococcus 
mastitidis, Galactococcus versicolor, G. fulrus, G. albus. 
