QUANTITATIVE MICROSCOPIC DETERMINATIONS 147 



Immature pollen grains (irregular in outline with conical projec- 

 tions of extine indistinct) abundant, 12,500,000 per gram or even more. 



Fibrous tissue should not exceed 25 per cent. 



Sclerenchymatous tissue is sparingly present. 



Ash should not exceed 5 per cent. 



Insect powder is extensively adulterated. The most common 

 adulterants are the stems of the plants (official species of insect flower) 

 from which the flower heads have been removed (fibrous tissue 80 to 

 90 per cent, with practically no pollen grains), flower heads of related 

 species of Chrysanthemum and of Pyrethrum, of Calendula, of Cha- 

 momile and of other species of plants. Japanese and Chinese insect 

 powders made from unknown species of Chrysanthemum and Pyrethrum 

 are used as adulterants (often as substitutes). Mustard hulls, cur- 

 cuma, flour, corn meal and other inert vegetable substances have been 

 used as adulterants. Fully matured (old) flower heads may be used 

 (sclerenchyma cells very abundant, abundant fibrous tissue with 

 pollen grains comparatively few and fully matured). Note that the 

 decision of the Department of Agriculture does not specify the "un- 

 expanded" or "partially expanded flower heads." 



To make the counts of the pollen grains, place 1 gram of the very 

 fine air dry, well mixed sample of the insect powder in a 25 cc. gradu- 

 ated cylinder, add 5 cc. of water, mix thoroughly, then add 2 per cent, 

 gum arabic solution up to the 10 cc. mark, making a dilution of 1-10. 

 Mix thoroughly by shaking for 20 seconds. Make the counts by 

 means of the hemacytometer, using the 1/250 cmm. areas of the count- 

 ing chamber. 



4. A Microscopical Method for Determining the Percentage of Flours 

 and Starches in Foods and Drugs. It is frequently necessary to ascertain 

 the proportions of different flours in a mixed meal, as in pancake flours, 

 compounds of flour and corn meal, of flour and buckwheat, etc., and 

 to determine the amount of cereal and starch filler in sausage meats, in 

 ice creams, in mince meats, in pies and pie stocks, in face and dusting 

 powders, in baking powders, in jams, in jellies, in powders, pills and 

 tablets, etc. The chemical methods are not only time consuming but 

 often unsatisfactory and in many instances wholly inapplicable. The 

 following microscopical method is simple, quickly carried out and the 

 results are sufficiently accurate for all practical purposes. 



(a) The Mixing or Suspending Solution. The liquid in which to 

 make the suspensions of substances to be examined shall be a 3 per 

 cent, filtered aqueous solution of pure gum arabic. Boiled distilled 

 water shall be used. A 20 per cent, sterilized stock solution may be 

 kept on hand from which the desirable dilutions can be made. 



