CHANGES IN FRESH 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 
body 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 very 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 
soluble 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. 
Coagulable nitrogen. — There is a marked decrease in this constitu- 
ent during the course of the experiment, the decrease being most 
rapid during the first 7 days. The sample incubated for 100 days 
contains only 19.76 per cent of the amount of coagulable protein in 
the fresh sample. However, these figures do not show the full extent 
of the transformation of coagulable protein into noncoagulable 
