MICROSCOPICAL EXAMINATION OF FLOUR. 5 
the grain from, and including, the aleurone layer outward, and also 
the germ tissues. Botanically, the bran consists of the pericarp, or 
fruit coat, and the aleurone layer. 
In order to discover any relation that might exist between the bran 
particles and hairs and the various so-called grades of flour, the 
microscopical method already partially described (page 3) was em- 
ployed to determine the number of bran particles and hairs ordinarily 
found, in varying amounts, in different classes of flours. This enu- 
meration consisted in methodically examining and recording all of the 
bran particles and hairs contained in any given slide. It is well to 
form the habit of always starting at the same point in the mount, 
as, for example, the lower right-hand corner of the slide. The slide is 
slowly moved by means of the mechanical stage, and all of the bran 
particles and hairs detected outside the edge of the cover slip counted. 
Each particle of spermoderm (with accompanying aleurone layer, if 
present), epicarp, cross-cell and intermediate-cell tissues, and hairs 
are given a value of one, no matter how small the particle or hair 
fragment may be, surface as well as transverse sections being included. 
After the region outside the cover slip is carefully scrutinized, the 
slide is moved over the width of the space between the ruled lines, 
and another strip of the mount examined and the offal 1 counted. A 
bran particle with hairs attached is counted as so many hairs instead of 
being recorded, for the sake of convention, with the bran particle 
count. Germ tissues were not enumerated. This procedure, as de- 
scribed, is methodically followed until the entire slide has been 
examined. 
SOURCES OF VARIATION IN METHOD. 
In order to study the reliability of the method aside from its practi- 
cal application to the examination of flour, a large number of tests 
were made having for their principal purpose the determination of the 
probable sources of variation and their extent. In considering this 
question it was recognized that there might be a variation due to one 
or all of the following factors: (1) Personal equation, including one 
analyst's variation in counting the same slide on different days and the 
variation between two analysts counting the same slide on the same 
day; (2) daily variation due to the condition of light, etc.; (3) slide 
variation due to limits of accurate weighing of the test portion of 
flour; and (4) the variation in homogeneity of the bulk sample. 
i For the purpose of this investigation bran particles and hairs were considered as constituting ttie 
