POWDERING VEGETABLE DRUGS 59 



other and more dependable characters for purposes of study and identi- 

 fication. The histological elements of drugs are not materially 

 changed, no matter what the changes in color, odor, taste and weight 

 may be. A careful microscopical examination is the only reliable 

 means of determining the identity of a powder, but here also difficulties 

 are met with, as will be explained in the following chapters. 



The methods of microscopic examination should be uniform for 

 the different powders, and great care is necessary to avoid confusion. 

 The examiner will not be able to obtain reliable results unless he is 

 familiar with the histology of plants and has the ability to recognize 

 different cell-forms in whatever position they may be found. For 

 microscopic examination the most suitable fineness is No. 40 to 60 

 for low powers and about No. 80 for high power work. Very fine pow- 

 ders, as No. 100 and finer, are rarely desirable for microscopic work. 



