CHANGES IF FKESH BEEF DURING COLD STORAGE. 23 



Soluble nitrogen. — The data under this heading simply show more 

 clearly changes that have been previously discussed in connection 

 with Table 9. There are at first marked decreases in the soluble 

 nitrogen in the samples incubated for 7, 14, and 21 days, after which 

 there are gradual increases in this constituent as the incubation 

 period progresses. The total increase in the sample incubated 100 

 days amounts to 22.12 per cent of the soluble nitrogen present in the 

 fresh sample. This increase is practically the same as the decrease 

 in soluble nitrogen in the sample incubated 7 days. 



The increase in soluble nitrogen in the incubated samples is 

 clearly due to the action of a proteolytic endoenzym, capable of at- 

 tacking native proteins and of working in an acid medium. The 

 presence of such an enzym in muscular tissues, as well as in other 

 bodj" tissues, is generally recognized. Vernon (1910) names such an 

 enzym " protease." A discussion of the factors limiting the total 

 extent of the action of this enzym upon the insoluble muscle proteins 

 is hardly within the province of this paper. 



The decrease in soluble nitrogen in case of the samples incubated 

 for 7, 14, and 21 days is harder to explain. The following appears 

 to be the most reasonable explanation of this condition. It is a well- 

 known fact that muscular tissue contains a much higher proportion 

 of soluble protein before rigor mortis has set in than after that 

 process is complete. Oppenheimer (1909) cites experiments where 

 87.3 per cent of the total protein of muscular tissue was found in 

 soluble condition before rigor mortis had set in, while only 28.5 was 

 present in the soluble form after rigor was complete. In our experi- 

 ments the fresh material was analyzed 24 hours after slaughter of 

 the animal, at which time rigor mortis was assumed to be complete. 

 The fact that the samples incubated for 7, 14, and 21 days show de- 

 creases in total soluble nitrogen as compared with the fresh material, 

 indicates ver}' clearly that rigor mortis was not complete when the 

 fresh muscular tissue was analyzed. It may be noted that while the 

 samples incubated for 7, 14, and 21 days show decreases in total 

 sohible nitrogen, as compared with the fresh material, the maximum 

 decrease was reached in case of the sample incubated 7 days, and 

 from that time on the change was in the other direction. This fact 

 indicates that the coagulation of muscle proteins, which accompanies 

 rigor mortis, was complete at the end of 7 days and probably at an 

 earlier date. 



f'oaf/vlohle nitrogen. — There is a marked d('(;rease in this constitu- 

 ent (lur-jng the course of the exf)erinient, the dcci-case being most 

 r;i|)l(| (luring the first 7 days. The sample incubated foi- 100 days 

 ffjiitains only 19.70 per cent of the amount of coagiilaldc protein in 

 the fi-esh sarnph*. However, these figures do not show tlici lull exl-cnt 

 of the tiiinsforniation of coagulable protein into noncoagulable 



