104 SCIENCE PROGRESS 



By the second method the bacteria may reach the interior 

 of the meat comparatively rapidly, and set up fresh centres of 

 infection within the meat. 1 



Fungi produce a somewhat characteristic degeneration of 

 the surface of the meat described as mouldiness. 



The changes bringing about the deterioration of meat at 

 ordinary temperatures are, then, chemical in nature. They are 

 either brought about by the meat itself in conjunction with 

 certain external conditions in regard to moisture and oxygen 

 supply, or are the result of the action of micro-organisms 

 (bacteria and moulds), living saprophytically on the meat. In 

 the preservation of meat in cold storage the object is, of course, 

 to prevent these changes as far as possible. 



In considering how low temperatures influence these pro- 

 cesses we must treat of chilled meat and frozen meat separ- 

 ately, as the problems involved are quite different in the two 

 cases. Chilled meat is usually stored at temperatures from o° 

 to 3 C. At these temperatures all the changes which take 

 place at higher temperatures also take place, but at a reduced 

 rate. As in the case of fruit, scope for variation in the method 

 is not great. The external factors which can be influenced are 

 again light and humidity. As regards light it is generally 

 held that meat should be kept stored in the dark, as the pre- 

 sence of light accelerates the actions resulting in rancidity of 

 the fat. In regard to humidity, a moist atmosphere favours 

 the growth of bacteria, while later, moulds appear on the sur- 

 face of the meat in abundance. On the other hand, if the 

 atmosphere is dry, water is lost from the meat by evaporation, 

 but it is regarded as an advantage if the surface of the meat 

 is harder and drier owing to water loss, as it renders the pene- 

 tration of micro-organisms slower and more difficult. 



Thus the principle involved in the preservation of meat 

 at low temperatures above the freezing-point is the reduction 

 in the rate of progress of a number of chemical actions. It 

 is obvious that the changes leading to deterioration of the 

 substance are not stopped, but are only slowed down, and 

 consequently there is a limit to the time in which meat can be 

 kept in this way without substantial deterioration. For sides 

 and quarters of beef this limit is about thirty days, although 

 sometimes the produce is kept for twice this time, or even longer. 

 1 Richardson and Scherubel, J. Ind. Eng. Chem. 1, 95, 1909. 



