30 QUEENSLAND AGRICULTURAL JOURNAL. [1 Jan., 1899. 
The bacteria that are of the most importance from a sanitary standpoint 
gain access to the milk in two ways:—(1) From a diseased condition of the 
cow ; (2) subsequent to the withdrawal of milk from the animal. 
No one will, willingly, consume milk from a diseased animal, yet it does 
not necessarily follow that the milk of all animals that are not in a condition 
of perfect health is not fit for use. Where the animal has a disease that also 
affects the human family, as in the case of tuberculosis, a danger exists that 
does not where the affection is confined to the bovine race. 
TUBERCULOSIS AND PUBLIC HEALTH. 
Perhaps more danger exists with reference to tuberculosis than with any | 
other animal disease. Its widespread distribution, its insidious development, 
and the not infrequent infection of the milk-yielding organs, makes this question 
one of great importance to public health. Since the introduction of the tuber- 
culin test, and the recognition of a greater prevalence of this disease than was 
heretofore supposed, the relation of this quality to the purity of public milk- 
suppliers has been made more prominent. While the extensive use of the 
tuberculin test is showing that the amount of bovine tuberculosis is much larger 
than was heretofore supposed, still it must not be considered that all animals 
that react to the test are actually in a condition where their milk supply is 
infectious. In much the larger number of cases of tuberculosis, the milk is 
entirely free from the specific organisms of this disease. Where the udder 
itself is involved, or where the disease is generalised throughout the lymphatic 
system, the milk very frequently contains disease germs in such quantities that 
infection of experimental animals results from the inoculation of small quantities 
of the milk. ' 
The difficulty is that these conditions cannot be determined with certainty, 
and, therefore, there is always an clement of uncertainty in using such milk. 
Then, again, suppose that the milk from a reacting animal was entirely free 
from contagious matter, how long would such a state continue is a question of 
practical importance. It not infrequently happens that an animal affected 
with a chronic latent type of the disease passes from such astage to a more 
acute condition, where the disease makes rapid progress. Such a change often 
occurs as a sequel tu some special tax on the system, as in calving, &e. 
Therefore the only positively safe rule, as far as public milk supplies are 
concerned, is to reject the milk of all reacting animals, unless it is first treated 
in a way so as to destroy any tubercle germs that might be present. 
There is another point that bears on the actual danger that exists in 
public supplies derived from mixed herds, and that is the influence of dilution 
of infected with healthy milk. The tubercle bacillus, unlike nearly all other 
disease-producing organisms, is unable to grow at ordinary air temperatures. 
It can tarive only at blood heat; therefore, if milk actually contains a certain 
number of tubercle organisms, these cannot increase in the milk after it is 
drawn from the cow. 
The dilution of contaminated milk with milk from a number of other 
animals frequently diminishes the amount of infective virus per unit of volume 
to such an equal extent as to deprive it of its infective properties. Where the 
milk supply is derived from a single cow, special care should therefore be 
taken to determine whether the animal has bovine tuberculosis or not. 
The conditions under which this disease is spread are of great importance, 
but this phase of the subject belongs more especially to a discussion of the 
as subject of bovine tuberculosis than to the relation of milk to public 
ealth, 
DISSEMINATION OF DISEASE BY CONTAMINATION OF MILK SUBSEQUENT 
TO MILKING. 
Milk affords a good culture medium for the development of a considerable 
number of disease germs that are unable to produce any diseased condition in 
the animal. These organisms gain access to the milk in a variety of ways, but, 
in general, they establish themselves through careless methods of handling the 
milk during, or subsequent to, its withdrawal. 
