700 
Journal of Agricultural Research 
Vol. V, No. is 
Percentage of meat digested. —In 0.5 gm. of meat the theoretical 
maximum amino nitrogen varies between 10 and 12 mgm. In order to 
convert the figures for amino nitrogen in Table XII to the percentage 
of the total amino nitrogen, it is only necessary to multiply them by 
a factor easily obtained mentally, which factor varies from 10 to 8.5. 
Thus, in experiment 32, 10 c. c. of the beef sample 11 digestion fluid 
contained 4.16 mgm. of amino nitrogen at the end of six hours. At 
complete digestion 12.39 mgm. would have been present; therefore 
4.16-M2.39 or 34 per cent of the total amino nitrogen present had 
been unlinked by the cleavage of polypeptids under the conditions of the 
experiment. The same figure may be obtained directly by multiplying 
in round numbers 4 by 8. A minute before, or after, this particular 
amino-nitrogen determination was begun, a 100 c. c. portion of the same 
digestion fluid had been neutralized by the addition of 24.5 c. c. of iV/5 
sulphuric acid. This mixture was brought to a boil in the next few 
minutes, filtered, and total nitrogen was determined in the filtrate and 
the precipitate. The results were recorded in Table XI. This table 
shows that in the same experiment, No. 32, at the end of six hours' 
digestion of beef sample 11, approximately 60 per cent (i. e., 31.7-^51.2) 
of the originally insoluble beef sample 11 nitrogenous substances had 
gone into solution as proteoses, peptones, and amino acids. These 
figures show how imperfect is the expression “Percentage of meat 
digested." The digestion process involves several chemical changes 
which take place at different rates. In general, the cleavage (by trypsin) 
of the larger molecules of alkali proteinate and proteose goes on at a 
comparatively rapid rate, the cleavage of the simpler peptone and poly- 
peptid molecules at a slow rate. These facts are illustrated by the fore¬ 
going data of experiment 32. By the second method of measuring 
digestion it was shown (Table XI) that at the end of six hours' digestion 
60 per cent of beef sample 11 had been transformed into proteoses, pep¬ 
tones, and amino acids; but by the third method of measuring digestion 
only one-third of the total amino nitrogen present had been unlinked 
(Table XII). The last two statements are correct; but it would not be 
entirely correct to say that according to the second method 60 per cent 
of beef sample 11 had digested at the end of six hours, or that 34 per 
cent of beef sample 11 under the same conditions had digested, using the 
third method of measuring digestion. A single figure can not describe 
several simultaneous processes in this case. The results in Tables XI and 
XII were obtained with the same digestion mixtures. The results in 
Table XII are expressed in milligrams of amino nitrogen obtained from 
10 c. c. of digestion fluid, equivalent to approximately 0.5 gm. of meat. 
Preservatives not used. —In all the digestion experiments the 
flasks in which the meat was heated and later digested were partly 
sterilized by the heating in the boiling-water bath. During the diges- 
