MAEKET COLD-STORAGE CHICKENS. 89 



single individuals may withstand unfavorable conditions. Repeated 

 freezing and thawing will completely exterminate some varieties, cer- 

 tain individuals of which will survive a single freezing and thawing. 

 The interesting observation is also made that spore formers are more 

 resistant than are vegetative cells. 



From the foregoing summary it would appear that a considerable 

 number of bacteria can, when the food supply is favorable, reproduce 

 at 0° C. or even below that temperature, though growth is greatly 

 retarded, and that freezing, even though prolonged, does not of neces- 

 sity indicate sterility. 



CHEMICAL CHANGES PRODUCED BY BACTERIA AT LOW TEMPERA- 

 TURES. 



For the purposes of this investigation the proof of the viability or 

 even of the reproduction of bacteria at low temperatures does not suf- 

 fice, since the changes taking place in certain foodstuffs kept in a 

 frozen condition are under consideration, which changes are funda- 

 mentally chemical. It becomes necessary, then, to investigate the 

 ability of bacteria, when maintained at low temperatures, to cause 

 changes in such compounds as proteins, carbohydrates, and fats, it 

 being commonly held that even if organisms should multiply under 

 such conditions the results of their life processes would not correspond 

 with those taking place at the optimum growth temperature. 



Muller a has studied the evolution of carbon dioxid, hydrogen sul- 

 phid, the breaking down of protein, and such chemical changes as 

 commonly accompany the growth of bacteria when the germs were 

 maintained at a temperature of zero. He finds that for organisms 

 growing at zero ach. chemical indications of activity are not wanting, 

 but that the formation of the various decomposition products is 

 greatly retarded and their production is very slow. Such results are 

 quite in accord with another observation of Miiller's, namely, that 

 the life cycle of one of the organisms isolated, B. fluoresceins liquefaciens, 

 at 0° C, is twenty-four times as long as is the cycle at 25° C. 



EFFECT OF LOW TEMPERATURES ON ENZYMES. 



On this most important phase of bacterial growth and development 

 there is almost a total lack of recorded observations, those changes 

 which have been traced chemically in flesh foods chilled or frozen being 

 ascribed to enzyme action exclusively. Undoubtedly enzymes play an 

 important role in these decompositions, but it is quite possible that 

 they are not the sole agency. Fermentation changes due to bacteria 



a Uber das Wachstum und die Lebenstatigkeit von Bakterien, sowie den Ablauf 

 fermentativer Prozesse bei niederer Temperatur unter spezieller Beriicksichtigung des 

 Fleisches als Nahmngsmittel, Archiv. Hyg., 1903, 47: 127. 



