DIGESTIBLE NUTRIENTS IN FOOD MATERIALS. 201 
referred to in the discussion of the subject of coefficients of 
digestibility in the preceding article, viz., that they have been 
made with single food materials, and the indications are that 
the digestion is less complete in these cases than it would be 
with ordinary mixed diet. In the article just referred to, the 
attempt was made to find coefficients of digestibility for the 
nutrients of different classes of food materials such as would, 
when applied to the constituents of ordinary mixed diet, give 
estimates for the quantities of digestible nutrients correspond- 
ing to the results of actual experiment with the same diet. 
From the data which had accumulated up to the present time 
coefficients of digestibility were assumed for the nutrients in 
different classes of foods, as explained on page 187. ‘These 
coefficients were afterwards applied to a series of actual 
digestion experiments, and the proportion of estimated diges- 
tible nutrients obtained by their use was found to agree 
almost exactly with those obtained by actual experiment. 
The differences, indeed, were in most cases hardly wider 
than are often found-in duplicate analyses of the same speci- 
men of a given food material, by different chemists following 
the same analytical methods. Such coincidences were observed 
in a considerable number of cases. And it would appear that 
they could be hardly possible unless the assumed coefficients 
were tolerably close approximations to the truth. It seems 
safe, therefore, to use these coefficients for tentative estimates 
for the digestibility of some of the more common food materials. 
This is done in table 61. With reference to the computations, 
however, two things should be clearly understood: 
First.—The estimates are only tentative and are subject to 
revision as information accumulates regarding both the com- 
position and digestibility of the food materials. It is worth 
noting, however, that the probable errors in the figures 
assumed for the coefficients are apparently less than the 
known variations in the composition of different specimens of 
food materials of the same kind. 
Second.—Some further distinctions need to be made between 
the coefficients of digestibility of different materials of the same 
general group. For instance, ordinary wheat flour, so-called 
‘entire wheat flour’’ or ‘‘ whole wheat,’’ and graham flour 
