8 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 
most strikingly shown. One false step, such as running pasteurized | 
milk through a piece of dirty cheesecloth before it enters the bottle — 
filler, may undo all the previous work. Pasteurization is an added 
expense, and merely as a matter of business, it is hard to believe that 
after the process is properly performed anyone would willfully al- 
low the results to be spoiled by a single operation, no matter whether 
the object of the process is to produce a sanitary milk or merely 
to preserve it. The failure of a few plants to pasteurize properly is 
no reason for condemning the process. In such cases a little educa- 
tion will often produce marked improvement and enable the milk 
dealer to meet city regulations. 
The control of the process of pasteurization should be based only 
on accurate scientific data. In the past it has often been the practice 
to expect a bacterial reduction of 99 per cent during pasteurization. 
While it is an easy matter to destroy 99 per cent of the bacteria when 
the raw milk contains large numbers, it is often impossible, on ac- 
count of heat-resistant bacteria which are not necessarily spore form- 
ers, to destroy 99 per cent when the milk contains about 100,000 bac- 
teria per cubic centimeter. In a large number of experiments in 
which milk was pasteurized under exact laboratory conditions, where 
no reinfection was possible, in one sample only 17 per cent of the 
bacteria were destroyed. Often 99 per cent of the bacteria may be 
destroyed, and yet the milk may still contain hundreds of thousands, 
while in other cases in which it contains only tens of thousands, the 
per cent of reduction may have been only from 80 to 90. The ef- 
ficiency of the process can not be based on the per cent of bacteria 
destroyed. 
In the control of pasteurization it is essential that the proper tem- 
perature be used and that the process be so performed that no rein- 
fection takes place. This can be accomplished best by direct super- 
vision of milk plants by trained men who have authority to carry 
on such supervision, and by bacteriological control of the process. 
HANDLING PASTEURIZED MILK. 
The pasteurization of milk destroys about 99 per cent of the bac- 
teria; consequently the milk is not sterile. On account of this fact 
pasteurized milk is still a perishable product, and must be handled 
with the same care as raw milk. This is a point for both the con- 
sumer and the milkman to remember. | 
Milk after pasteurization should be cooled to about 40° F. and | 
kept at that temperature until delivery. During warm weather it 
should be.iced on the delivery wagons. From a sanitary standpoint — 
all milk, whether raw or pasteurized, should be delivered as soon as | 
possible, in order that the consumer may get it in the best condition. 
