72 DEPARTMENT OF AGRICULTURE. 



fectly explored fields may be expected in proportion as observers resort more and more to 

 the practice of preserving in a permanent way the type specimens which serve as a basis 

 for their descriptions, and in proportion as photographs are substituted for those half- 

 schematic or diagramatic drawings, which represent rather the interpretation of the inves 

 tigator than the objects as they exist in nature. But perhaps even more is to be antici 

 pated from the application of new reagents, and of improved modes of preparing the tis 

 sues for microscopic examination. When we reflect on the extent of the additions 

 which have been made to our knowledge of minute anatomy by processes quite recently 

 introduced, such as imbibition with nitrate of silver, chloride of gold and osmic acid, 

 the preparation of thin sections of frozen tissues and the use of the moist chamber, 

 it is impossible to resist the conclusion that it is from future improvements in this direc 

 tion that solid progress in the normal and pathological histology of the lung is chiefly to 

 be expected. 



Very respectfully, your obedient servant, 



J. J. WOODWARD, 

 Assistant Surgeon and Brevet Lieutenant Colonel United States Army, 



in charge of the Medical and Microscopical Sections of the Museum. 

 Brevet Major General J. K. BARNES, 



Surgeon General U. S. Army. 



