8 4 



MICROSCOPICAL DIAGNOSIS. 



numerous. Thirty or forty rings can frequently be counted in one 

 grain, while potato-starch sometimes has only three or four. Arrow- 

 root starch takes a distinct cross with polarized light It is very fre- 

 quently adulterated with potato starch. 



Wheat Starch. Pure wheat starch can be obtained by cutting 

 through a kernel of wheat, and scraping with the point of a knife a 

 little from the central part of the kernel on a glass slide. There are 

 two distinct kinds of grains found here ; small spherical or angular 

 grains floating frequently in a mass, many times more numerous 

 than the large grains, and about 5 Vo f an mc ^ m diameter. The 



others are large, lenticular grains, which, when viewed on the face, 

 appear like a spherical grain. When viewed on the edge, they have 

 the appearance of a double-convex lens. This lens shape can easily 

 be proved by touching the cover glass gently with a pencil-point, and 

 watching the grains roll over in the field. This should always be 

 done when testing for adulterations with starch grains. There is 

 seldom any nucleus, but when it is present it is central, and still 

 more seldom are there any rings. When viewed with polarized light, 

 only a faint cross is seen if any.* When subjected to dry heat, the 

 grains are changed very much in appearance; being warped consider- 

 ably from their normal shape. They are larger, more brittle, and 



*The statement is made by sime botanists th.u wheat starch gives a cross under polarized 

 light, but I have never been able to detect any closer approach to one than a nearly uniform 

 shadow floating over the grain. 



