160 POWDERED VEGETABLE DRUGS 



count as in the substance under examination, then we would know 

 that the sand adulteration amounted to 50 per cent. However, in the 

 case of sand adulteration, the simpler and almost equally accurate 

 beaker or test tube sand test will be employed, rather than the 

 microscope. 



The depth of the mount, namely 0.2 mm., requires good working 

 distance of the compound microscope in order that the entire depth 

 may be brought into view. The cover glass used must be thin, not to 

 exceed the thickness of the ordinary No. 2 covers. The usual lense 

 combination (qcular and objective) giving a magnification of about 

 350 to 500 diameters may be used. A good observer who is entirely 

 familiar with tissues and tissue elements could use a lower magnifica- 

 tion with better effect, such as a well corrected combination giving a 

 magnification of about 180 diameters. 



The procedure is as follows: Carefully examine each and. every 

 separate and distinct field, counting all of the characteristic tissue 

 elements, and record the findings numerically. The mechanical 

 stage will be of advantage in shifting the counting chamber. It will 

 be found that from thirty to fifty distinct fields can be counted in 

 one mount. The averages of not less than fifty counts should be 

 taken upon which to base the percentage estimates of quality or 

 adulteration. 



Before beginning the counts, it is advisable to look the mount over 

 under the low power (about 90 diameters) for the purpose of ascertain- 

 ing whether or not the material is uniformly distributed. If it is 

 unevenly spread, a new mount should be made. In fact, the low power 

 alone is used in examining some substances, as for example Cinchona 

 bark, the identity and purity determinations of which are based upon 

 the counting of the characteristic large bast elements. Difficulty 

 may be encountered in getting the total counts of aggregates of cells, 

 as bast and sclerenchyma. As a rule, however, in a number 80 powder, 

 aggregates which are so large as to make counting difficult are rare. 

 Some investigators have suggested that the quantitative estimates 

 should be based upon the actual measurements of cells and cell con- 

 tents. This is not necessary, as the average of the numerical count is 

 fully as accurate as the average based upon measurement. However, 

 as already indicated, where identity depends upon differences in size, 

 then measurements (linear) must be made. 



It is necessary that the same microscope and the same objectives 

 and ocular be used at all times, in order that the results may be re- 

 latively uniform. For instance, should a partial count be made with 

 one instrument, and completed with another instrument, even if 



