iv PREFACE TO FOURTH EDITION. 



small quantities of powders, or from a few drops of an extracted 

 solution as obtained in assay work. While there are a number 

 of books treating of micro-chemistry, yet the treatment of the 

 microscopic crystals in these is of a general character. The 

 only satisfactory way to study these crystals is by means of the 

 petrographical microscope. In Part IV about forty pages have 

 been included treating of the micro-analysis of some of the 

 important plant constituents, and it is believed that this portion 

 will be especially useful in the detection and accurate study of 

 these substances. In the preparation of this part the author had 

 the hearty cooperation of Dr. Charles Travis, of the University 

 of Pennsylvania, who not only made careful studies of the 

 crystals described, but read the proof very carefully. 



The new illustrations include some thirty-five photographs 

 of microscopic crystals ; a four-color plate, made from Lumiere 

 autochrome photographs, showing salicin and cocaine hydro- 

 chloride under the micro-polariscope, with crossed nicols; and a 

 number of half-tone illustrations and drawings of medicinal 

 plants. In addition, the work has been brought up to date by 

 including the results of the researches published during the past 

 two years. 



Acknowledgment is cheerfully made to the editor of Merck's 

 Report for permission to use some of the excellent drawings 

 from Dr. Theo. Holm's articles on " Medicinal Plants of North 

 America." 



H. K. 



September, 191 o. 



