and Laboratory Methods. 'i577 



iron. Under the impetus given to such applications by the work of such men as 

 Moeller, Schimfer and others, many of our colleges and technical schools have 

 courses involving practical applications of the instrument to certain branches of 

 the trades and applied sciences. 



Unfortunately, however, for the average American worker, the greater part 

 of the literature upon the subject is in German or French. Although we cannot 

 be expected to go exhaustively into the subject in such a series of papers as is 

 here contemplated, yet letters of inquiry which the writer has received have led 

 to the conclusion that the sources of such information are not widely known even 

 among those who desire to know concerning the subject, to say nothing of that 

 other class of individuals to whom the value of applied microscopy in the indus- 

 tries has never occurred. It is with a view to being of some service to these two 

 classes of persons by collecting such material as may be available and putting 

 into convenient form for the average beginner, that this series has been under- 

 taken. 



In the description of methods and technique we may treat the subjects from 

 an elementary standpoint, but this fault will perhaps be pardoned in view of the 

 fact that it is intended to be of service especially to the beginner in this line of 

 work. 



It may be well for the worker to bear constantly in mind that the use of the 

 microscope is merely applied microscopy, that the basis of the whole subject lies 

 in a knowledge of scientific facts, and the broader this knowledge the greater 

 will be the ease with which results can be obtained. It really consists of glean- 

 ings in the scientific field gathered for a special purpose. 



The greater portion of the substances which we have to deal with are directly 

 or indirectly of vegetable origin. Hence it is quite necessary that the worker 

 have a general idea of structural botany. Almost any of the textbooks upon 

 elementary botany give some attention to this branch of the study and will be 

 of service. 



Familiarity with the subject can only be gained by actual practice, — no 

 amount of reading or examination of ever so accurate illustrations can take the 

 place of personal examination of the substances themselves. Such can serve 

 only as sign boards or danger signals, while the most intimate acquaintance of 

 the features of the road must be gained by actually traveling over it. 

 U. S. Department of Agriculture. BuRTON J. HoWARD. 



