G. S. WILSON, F. C. MINETT AND H. F. CARLING             57

vaccinated the same month with a living vaccine, since when there has not been a
single case of abortion. At a herd test carried out some time before the com-
mencement of this experiment, no animals showed the presence of specific agglu-
tinins in the blood.

Johne's disease has seldom occurred; the last animal to be affected with it
was in September 1929.

The herd has always been relatively free from udder troubles. In October
1936, at the conclusion of the feeding experiment, the milk of each cow was exa-
mined culturally by plating in ox-blood agar, with the result that of the eighteen
animals present three were found to be affected with streptococcal mastitis in a
subclinical form.

Pasteurizer.—To ensure a supply of adequately pasteurized milk, it was decid-
ed to pasteurize the milk on the premises; A small batch pasteurizer, of 2-gallons
working capacity, fitted for low-pressure steam heating, was specially manufac-
tured for us by Messrs. Brown and Son, Ltd., London, N. 19. It was made of
copper, coated with pure tin, and consisted of an outer steam-heated jacket and
an inner vessel, to hold the milk, which could be lifted out for cleaning and steriliz-
ing purposes. It was provided with an overhead motor-driven agitator and an
auto-thermostatic control. In practice the milk was heated up till the indicator
thermometer, which dipped into the milk itself, registered 145°F. (62.8°C.). The
temperature was maintained at this level for 30 minutes, after which the steam
was turned off. The milk was then cooled, either to 90°F. (32. 2°C.) if it was to be
fed immediately to the calves, or to the temperature of the tap water if it was to
be kept for some hours.

The milk.—The mixed milk of the herd from the morning's milking alone was
used. The required quantity was divided into two parts. One part was pas-
teurized at once at 145°F. (62.8°C.) for 30 minutes ; the other half was left raw.
Part of the raw and part of the pasteurized milk were fed at a temperature of about
90°F. (32.2°C.) to the calves in the morning. The remainder of the raw and pas-
teurized milk was water-cooled and kept in covered pails in a cool dairy till the
evening, when it was warmed to about 90°F. and fed to the calves.

Though this was the routine practice throughout the greater part of the ex-
periment, a misunderstanding occurred at the commencement which was responsi-
ble for some trouble during the first six months. Instead of the milk, immediately
after pasteurization, being divided into two parts, one part being cooled to 90°F.
and fed to the calves in the morning, the other part being cooled to tap-water
temperature and kept for the evening feed, the whole of the pasteurized milk was
cooled only to 90°F., and the part for the evening feed was left to cool down slowly
in the dairy. As a result considerable bacterial multiplication occurred in the

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