696 BOTANY AND PHARMACOGNOSY. 



drug like aloes is sold in place of the genuine drug. In some 

 cases, as in that of ground flaxseed, an attempt is made to supply 

 the deficiency in oil of the exhausted product by adding a petrol- 

 eum oil. In the case of a number of drugs, such as rhubarb, 

 licorice and belladonna root, much of the commercial powder 

 consists, in part at least, of the exhausted powder. In order to 

 guard against the use of exhausted drugs there is a disposition 

 to lay considerable stress upon the amount of extractive 

 (aqueous, alcoholic or ethereal) yielded by different drugs. 

 In many instances drugs that are worm-eaten, or admixed with 

 other drugs or plant parts, are used in the preparation of powd- 

 ered drugs. 



Reagents. — For the rapid differentiation and study of the 

 characteristic tissues and cell-contents of the powder it is neces- 

 sary to employ reagents which render the particles more or less 

 transparent and at the same time do not destroy their characters. 

 The most satisfactory reagent of this kind for general purposes is 

 an aqueous solution of chloral or a solution of chloral and glyc- 

 erin ; about a milligram of the powder is mounted in a few drops 

 of the solution, the preparation is gently heated, then allowed to 

 cool, and examined ; if it is not sufficiently transparent, it is heated 

 again. The reagent causes a swelling of the cell-wall and is not 

 applicable in the study of starch grains, but it is very useful in the 

 study of mechanical tissues, hairs and calcium oxalate. 



After having determined the presence of starch, a separate 

 mount of the powder in water is made and the size and markings 

 of the grains noted. 



For the examination of more or less lignified cells, mounts 

 are made, either in phloroglucin or aniline sulphate solution; in 

 some cases it is advantageous to apply these solutions after the 

 specimen has been previously treated with chloral. Sometimes it 

 is desirable to study the mechanical cells more closely, and 

 Schulze's macerating fluid (p. 188) may be used for isolating 

 them. 



Examination. — Before making a microscopical examination 

 of coarsely comminuted oir powdered drugs or foods it is desirable 

 to mix a small quantity of the material with a little water con- 

 tained in a watch crystal or small beaker and note such features 



