MICROSCOPICAL EXAMINATION. 



By B. J. HOWARD, 

 Chief, Microchemical Laboratory. 



GENERAL REMARKS. 



The microscopical examination of the stock foods offers more com- 

 plicated features than that of human foods because of the contamina- 

 tions which are commonly present. These are due to one or more of 

 three causes: (1) The use of screenings and other by-products; 

 (2) the use of low-grade grains containing more or less weed seed; 

 and (3) the willful addition of foreign matter as a makeweight. The 

 results obtained in the investigation indicate that the last named is 

 the least common form of adulteration. 



The wide diversity of materials which are used in stock foods and 

 which are susceptible of microscopic detection, as well as the vast 

 array of weed seeds which may be present to greater or less extent, 

 offers for the microscopist a wide field if he is to treat the subject com- 

 prehensively. 



The literature upon the microscopic examination of human food3 

 and drugs covers part of the field; but there is no publication upon 

 this subject alone, either original or compiled data, in convenient 

 form for the average worker. To cover the field fully would be 

 impracticable in a report of this nature, but it seems important to 

 give some attention to the structure of the principal ingredients and 

 the most important of the weed seeds which have been observed. 

 Most of the weed seeds may in small quantities be considered harmless 

 to stock, but a few are sufficiently poisonous when present in consid- 

 erable amounts to produce serious results. To this last class belong 

 seeds of fhe jimson weed (Datura stramonium L.), corn cockle (Agro- 

 stemma githago L.), and darnel (Lolium temulentum L.). 



APPARATUS, REAGENTS, AND METHODS. 



The methods used 'in performing this work are for the most part 

 simple in their technique. The apparatus consists first of a suitable 

 microscope giving a magnification of from 75 or 90 for the low power 

 up to a combination giving \\\ least 200. 



It was rarely found necessary to exceed this, though some workers 

 prefer somewhat higher power. A supply of microscope slides of 

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