tubercle bacillus in its vegetative stage is endowed with powers of
resistance greater than those possessed by any other pathogenic
organism. This work has not been substantiated by the most recent
investigations on this subject. In determining the thermal death point
of this organism, as of any other, not only must the temperature be
considered, but the period of exposure as well, and where that exposure
is made in milk, another factor must be considered, viz., the presence
of conditions permitting of the formation of a "scalded layer," for as
Smith[91] first pointed out, the resistance of the tubercle organism
toward heat is greatly increased under these conditions. If tuberculous
milk is heated in a closed receptacle where this scalded membrane cannot
be produced, the tubercle bacillus is killed at 140 deg. F. in 15 to 20
minutes. These results which were first determined by Smith, under
laboratory conditions, and confirmed by Russell and Hastings,[92] where
tuberculous milk was heated in commercial pasteurizers, have also been
verified by Hesse.[93] A great practical advantage which accrues from
the treatment of milk at 140 deg. F. is that the natural creaming is
practically unaffected. Of course, where a higher temperature is
employed, the period of exposure may be materially lessened. If milk is
momentarily heated to 176 deg. F., it is certainly sufficient to destroy
the tubercle bacillus. This is the plan practiced in Denmark where all
skim milk and whey must be heated to this temperature before it can be
taken back to the farm, a plan which is designed to prevent the
dissemination of tuberculosis and foot and mouth disease by means of the
mixed creamery by-products. This course renders it possible to utilize
with perfect safety, for milk supplies, the milk of herds reacting to the
tuberculin test, and as butter of the best quality can be made from
cream or milk heated to even high temperatures,[94] it thus becomes
possible to prevent with slight expense what would otherwise entail a
large loss.

_2. Dilution._ Another method that has been suggested for the treatment
of this suspected milk is dilution with a relatively large volume of
perfectly healthy milk. It is a well known fact that to produce
infection, it requires the simultaneous introduction of a number of
organisms, and in the case of tuberculosis, especially that produced by
ingestion, this number is thought to be considerable. Gebhardt[95] found
that