76 The N.Z. Journal of Science and Technology. [April 
action of naturally occurring enzymes present in fresh flesh foods. The 
alteration in the structure of the fibres of meat is associated with the 
freezing and subsequent thawing. 
By enzymic action is understood the action of a certain well-known 
class of substances normally present in all animal tissues and organs. The 
most commonly known enzyme is pepsin, which is capable, under favour¬ 
able conditions, of digesting proteins. 
In both fresh and frozen meats an enzyme has been found which is 
capable of bringing about slowly the limited changes found to take place 
under cold-storage conditions. 
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 for bacterial invasion. As bacteria are 
almost universally present in the ordinary atmosphere, it is to be expected 
that on the surface of meat there will be found bacteria, and that if the 
meat is allowed to remain unprotected the bacteria will spread to the 
interior. 
A vast amount of experimental data has been recorded upon the subject 
of'|the bacterial invasion of meat, and it has been clearly demonstrated 
that under the conditions of thorough and properly maintained cold storage 
(2° to 19° F.) there is no bacterial infection of the interior of initially sound 
meat, even after a period of two years’ cold storage. 
It is a matter of general observation that w r hen meats are frozen and 
thawed out rapidly a certain amount of distortion and rupture of the 
tissues may take place, and by some observers this has been accepted as 
evidence of decomposition of the meats, a conclusion which is not warranted 
unless supported by chemical and bacteriological experiment to prove the 
suggestion of putrefaction. Usually when the freezing and thawing are 
slowly conducted little or no alteration of the structure of the tissues will 
be found. A fact to be taken into consideration, however, wdien the 
freezing or subsequent thawing has produced rupture of the tissues is that 
the cell-walls have been broken, and so the meat-iuices, which are normally 
covered by an envelope of tissue, escape, and provide a nutrient medium 
upon which the bacteria present in the atmosphere can grow T luxuriantly 
and so bring about a very rapid decomposition of the meat when exposed 
to the ordinary temperatures of the atmosphere. 
In general, it is the practice after slaughter to allow the so-called animal 
heat of the carcase to dissipate before the meats are placed in cold storage. 
This is sound from the point of view of economy, for obviously it is more 
economical to allow the carcase to cool to the temperature of the atmosphere 
prior to placing it in the freezing-chamber than to utilize the artificial cold 
to reduce the temperature to that point before freezing. 
Despite the fact that the flesh of healthy animals is free from bacteria, 
the micro-organisms of putrefaction are almost universally present in 
the air, and the flesh is a suitable medium for their growth. The putre¬ 
faction of flesh foods is invariably due to bacterial growth, and if these 
foods remained sterile no putrefaction would result. As, however, it is 
not commercially practicable to render meat intended for cold storage 
sterile—that is to say, by the elimination of all the bacteria in the air-— 
the only course is to bring about a condition which prevents bacterial 
growth—namely, freezing as soon as is possible under the conditions which 
the particular factory or store have to meet. 
The results of many investigations have clearly shown that when taint 
and decomposition have taken place in cold-storage meats it is very 
definite evidence either that the meat had not been placed in cold storage 
