166 POWDERED VEGETABLE DRUGS 



be made by the student under the direction and guidance of the instruc- 

 tor. Each problem will require at least one full laboratory period. 

 The -exercises are graded, beginning with a few simple percentage de- 

 terminations of simple powders, the microscopical characteristics of 

 which are easily recognized, and ending with the percentage determina- 

 tion of a compound powder. By the time the student has worked out 

 the ten problems very carefully, he will be in position to solve any 

 ordinary problem in vegetable drug adulteration. 



The work done by the members of the class should be compared 

 and discussed and the differences in results should be accounted for 

 by the instructor in charge. If the work of the students has been 

 carefully done the percentage differences based upon the counting meth- 

 ods should not exceed 5. If the percentage differences exceed 5 the 

 exercise should be repeated. The personal factor must be carefully 

 considered. The instructor in charge must explain each problem 

 very carefully and in great detail and no student should be allowed 

 to begin upon the counts until it is ascertained for a certainty that he 

 understands fully what the problem is and what the count which he is 

 about to make, represents. He must know why it is that only one 

 or two tissues of each drug are selected for the purpose of making the 

 percentage counts. The various quantitative microanalytical methods 

 which have been proposed should be explained and discussed and the 

 advantages and disadvantages of the several methods explained. The 

 results of the microanalytical method herein recommended should be 

 compared with the results of the more commonly employed chemical 

 methods. Such a comparison will demonstrate that the percentage 

 results by the microanalytical methods are fully as accurate as the 

 percentage results by the usual chemical tests and analyses, as carried 

 out by analysts of about equal qualifications and experience. 



1. Cinchona Bark.- Reduce an absolutely pure average sample of 

 Cinchona Ledgeriana and of C. succirubra to a No. 80 powder. Make 

 1-5 suspensions in the manner already explained and by means of the 

 special counting chamber determine the average number of bast cells 

 per field. Take the average of not less than fifty counts of not less 

 than two mounts. The average of the counts thus obtained represents 

 the number of bast cells in a pure 100 per cent, cinchona bark. The 

 individual bast cells should be counted. Thus a group of three bast 

 cells should be counted as three. No attention is given to the bark 

 parenchyma cells nor to the sparingly present sclerenchyma cells. In 

 this particular exercise the percentage difference of the counts by the 

 students should not exceed 1 per cent. 



Make percentage mixtures of cinchona bark, using absolutely pure 



