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. 



1 For the purpose of this investigation bran particles and hairs were considered as constituting tlie 

 offal. 



