1920.] Wright.—Bacteriology in relation to Meat Products. 211 
The fact that the ends of a can may be bulged does not necessarily 
mean that the contents are spoiled : if the can is sealed without pre¬ 
liminary heating, or if it is overfilled, the ends may bulge while the contents 
remain sterile. Notwithstanding this, however, a bulged end on a can 
may safely be regarded by the consumer as a “ warning sign.'’ 
In the popular Press warnings are sometimes given against storing 
food in the open can after part of the contents has been removed, and 
often the most extravagant statements have been made on this subject. 
It should be obvious that an open can is as suitable for the storage of 
food as a tin receptacle of any sort in which most of the milk-supply is 
held daily. The amount of tin taken up by a food in the one or two days 
for which it is possible to store food in an open can is very much less 
than the amount taken up from the closed can between the time of canning 
and the time it reaches the consumer. Obviously, bacterial spoilage does 
not occur more readily in an open can than in an open glass dish. 
Contrary to the opinions held by certain authorities, solid meat-extract 
has been demonstrated by bacteriological methods to be a non-putrescible 
substance, and not to be subject to bacterial spoilage. ft has been found 
to possess properties inhibitory to bacterial growth. These properties are 
probably associated with its concentration, its salinity, and also with its 
acidity, for normal meat-juice possesses a marked amount of acidity, due 
to the presence of organic acids and of inorganic acid salts, which increase 
in proportion to the concentration of the meat-juice as it is evaporated 
down in the preparation of the solid extract of meat. 
Frozen Meats. 
Low temperatures have been used by mankind from the earliest times 
to preserve food from deterioration. While low temperatures suspend 
bacterial activities, they are not very effective in actually destroying 
organisms, for it has been demonstrated experimentally that extremely 
low temperatures injure bacteria only after prolonged exposure. 
There is evidence that the flesh of a mammoth incrusted in polar ice, 
and presumably thousands of years old, has been found to be intact, for, 
as stated by Nordenskj old in his book The Voyage of the Vega , it appears that 
the remains were uncovered by the moderation of the weather of northern 
Siberia, which resulted in land-slides and the disclosure of this mammoth, 
the flesh furnishing food for wolves and birds of prey. It is a remarkable 
testimony in favour of preservation by freezing that animal flesh and tissue 
structures should be preserved at all after the lapse of the thousands of years 
since the animal died. 
It is now recognized that the flesh of healthy animals is free from 
bacteria, but as soon as death ensues, if no measures are taken to guard 
against bacterial infection, the flesh becomes a suitable field of bacterial 
invasion and growth. As bacteria are almost universally present in the air, 
it is to be expected that on the surface of meat bacteria, will be found, and 
that if no measures are taken to prevent invasion of the interior bacterial 
growth will take place there. 
It has been found that bacteria and moulds are from a practical stand¬ 
point the existing causes of the principal changes which occur in flesh foods, 
and if these micro-organisms are absent, or their activities suspended, the 
changes in flesh food will be slow and inconsiderable. 
The fact that bacteria are able to withstand exposure to intense cold 
is of slight importance when placed beside the other fact, well established, 
