516 SECTIONAL TRANSACTIONS.—M. 
Dr. F. C. Minetr.—The Importance of Studying the Diseases of the Cow’s 
Mammary Gland. 
The subject is considered from three points of view, viz., from the agricultural, 
public health and pathological aspects. 
The Agricultural Aspect.—The diseases of the udder, which are included under 
the term ‘ mastitis,’ owe much of their importance to their wide prevalence. The 
most common form of mastitis, caused by a certain variety of streptococcus, follows 
a chronic and insidious course. In the larger milking herds it is probably correct to 
say that on an average not less than 25 per cent. of the cows are affected with this 
form in at least one quarter of the udder, the disease being especially prevalent among 
the older cows. The main reason why the losses from this source are not more clearly 
recognised is because most cases of chronic streptococcus mastitis remain latent or 
occult for long periods, and only at times give rise to clinical disturbance. Nevertheless, 
there is usually slowly progressive destruction of the milk-secreting tissue, so that in 
the aggregate the reduction in milk yield must be heavy. In addition, the milk 
from diseased quarters is often altered in quality, although at the same time there 
may be no important alteration in its appearance. Such milk is unpalatable and 
may also be unfit for the manufacture of butter and cheese. 
The effect upon the animal has also to be considered. Among the consequences 
of mastitis may be mentioned the depreciation in the value of the affected animals, 
the expense of maintenance and of treatment, and the excessive herd wastage. 
Moreover, certain forms of mastitis spread by contagion, so that the diseased animal 
is a source of danger to its companions. 
The Public Health Aspect.—Apart from the question of specific milk-borne disease, 
e.g. tuberculosis, attempts at providing a pure milk supply have been chiefly concen- 
trated in the past upon clean methods of drawing the milk and upon measures for 
reducing its subsequent contamination. From the public health standpoint there 
are several reasons why, except in the case of tuberculosis, comparatively little , 
attention has been paid to the diseases of the producing animal. So far as mastitis 
is concerned, one of the main reasons for this neglect is that the streptococci, which 
are the common cause of this condition, are harmless when ingested by human beings. 
While opinion on this point may now be said to be fairly unanimous, milk containing 
such bacteria and the products of tissue reaction cannot be regarded as a desirable 
food, even when diluted with normal milk. 
In several respects our knowledge of the importance of the animal factor in 
connection with the problem of a pure milk supply is looked upon as incomplete. A 
similar remark can be made in the case of the epidemiology of milk-borne outbreaks 
of scarlet fever and septic tonsilitis. With regard to the origin of these milk-borne 
diseases, the evidence on many occasions has pointed strongly to heavy and continued 
contamination of the milk, such as could only occur at its source. The suggestion 
that such outbreaks may originate through actual multiplication within the udder 
of pathogenic streptococci derived from human beings has been supported in a few 
instances by direct proof. More rarely there have been encountered cases of mastitis 
due to hemolytic streptococci, indistinguishable from those which are recognised to 
ee 
be capable of causing disease in human beings. At present the significance of this — 
observation is not clear, since as a rule there has been no history of illness among 
persons in contact with the cows. 
The Pathological Aspect.—Bacteria, e.g. Br. abortus, streptococci, derived from 
other situations in the animal body, sometimes localise in the mammary tissue and 
produce disease. Thus, bacteriological studies, including in their scope the udder — 
and its secretion, may contribute towards a clearer understanding of disease processes 
occurring in other parts of the body. i 
Reference is made to the possibility of using the mammary gland for investigating — 
under natural conditions the properties of bacteria and the relations which exist — 
%) 
between bacteria and living tissues. 
Finally, an assurance that the gland is in a state of health may be regarded as — 
essential for the scientific interpretation of the influence of various factors, such as 
heredity, breed and nutrition, upon the yield and composition of milk. ' 
