PART IV. MICRO-ANALYSIS. 



I 



The value of the microscope is well established in the exami- 

 nation of drugs, foods and technical products. In the preceding 

 pages the greatest prominence is given to the anatomical or 

 HISTOLOGICAL METHOD of analysis, based largely upon the study 

 of the form of cells, and the structure and composition of cell 

 walls. In a number of instances, the study of cell-contents, as 

 of starch grains and crystals of calcium oxalate, affords as was 

 seen an important clue to the identity of a product. There are, 

 however, many plant substances which are found in a crystalline 

 condition in the living plant and commercial product 

 and in the preparations made from them. A number of books 

 have been published dealing with the micro-chemistry or histo- 

 chemistry of some of these substances. For the most part the 

 study of these microscopic crystals has been of a very general 

 nature, in that statements are given regarding the general shape A 

 of the crystals or their aggregates and their behavior with 

 certain test solutions. The time has come when the study of 

 the crystalline substances found in drugs and their preparations 

 requires, if any real progress is to be made in this direction, 

 that the crystallographic method of analysis be introduced 

 into pharmacognosy. This method originated in the examination 

 of thin sections of rocks and it has been possible by this study 

 to identify the numerous rock-forming mineral species. In 

 those species which are mixed crystals, i.e., made up of isomor- 

 phous mixtures of two or more components, it has been possible 

 to determine with some accuracy their composition simply by 

 their optical properties, as for example the feldspars. Further- 

 more, it has been possible to draw conclusions as to the ultimate 

 composition of rocks and the conditions under which they were 

 formed. 



The value and possibilities of the employment of the crystal- 

 lographic method in biological studies is well exemplified in 

 the recent work of Reichert and Brown, " The Crystallography 

 8i6 



