POPULAR SCIENCE 103 



the first change which takes place is the setting in of the con- 

 dition called rigor mortis, during which the muscle fibres lose 

 their contractility. The soluble proteins coagulate, lactic acid 

 is produced and the reaction of the meat changes from alkaline 

 to acid. Later, the condition of rigor mortis passes away as 

 the muscle tissue undergoes a fresh change, that known as 

 " ripening," in which the muscle tissue relaxes, the meat at 

 the same time becoming more tender. This change is brought 

 about by proteolytic enzymes in the meat, and is to be re- 

 garded as a process of auto-digestion. At the same time, as 

 the process of ripening is proceeding in the lean, other changes 

 are proceeding in the fat. This latter undergoes hydrolysis 

 if water is present, by which fatty acids and glycerol are pro- 

 duced, while, in presence of oxygen as well, lower fatty acids, 

 aldehydes and other volatile substances are formed, producing 

 the unpleasant condition known as rancidity. 



These changes take place slowly at ordinary temperatures 

 if the necessary external conditions (water and oxygen) are 

 present, as under ordinary circumstances they always are. At 

 temperatures of from i° to 3 C. the maximum "ripening" 

 effect in sides and quarters of beef is reached in from fifteen to 

 twenty-One days, when a secondary complication has not 

 affected the meat to any extent. This complication results 

 from the invasion of the meat by micro-organisms (bacteria and 

 moulds). The progressive decomposition of lean meat brought 

 about by micro-organisms is that which is generally responsible 

 for its becoming spoilt, the changes being described as putre- 

 faction or decay according as they are produced in absence or 

 presence of oxygen. The former changes are characterised 

 by the production of unpleasant smelling substances ; these 

 are practically absent in the latter, but much carbon dioxide 

 is given off. 



Hydrolysis of fat may also be brought about by bacterial 

 action, but is usually negligible. 



The penetration of bacteria into meat takes place in two 

 ways. There is a gradual and regular progress inwards of the 

 original surface colonies, and a more rapid and irregular pene- 

 tration along the connective tissue. In the case of the former, 

 penetration at a temperature of about 2° C. is from 0*2 mm. to 

 1 cm. in thirty days ; naturally the distance of penetration 

 increases with the time stored. 



