EXTRANEOUS MATTERS. 



the use of glass shades and other means, we often 

 preserve portions of hair, feathers, scales of the 

 wings of insects, and a number of other foreign bodies 

 which we would gladly exclude from our prepara- 

 tions. The characters of these organic particles 

 are but too well known to us, and probably hun- 

 dreds of microscopists have many times examined 

 the dust which commonly collects upon shelves and 

 little projections from the walls of our rooms, for the 

 very purpose of demonstrating the many different 

 kinds of organic fragments of which it is in great part 

 composed. Memoirs have been written upon the 

 extraneous matters which fall into urine, sputum, and 

 other secretions which it is the business of the physi- 

 cian to examine. These extraneous particles which 

 have been deposited from the dust suspended in the 

 air of the rooms have given rise to great confusion, 

 and some of them have been mistaken for bodies 

 derived from the organism of man. No wonder, there- 

 fore, that much attention should have been given to the 

 examination of dust, and in order to prevent mistakes 

 figures of some of the most important constituents of 

 dust have been given.* Particles of hair and wool of 

 various kinds, filaments of cotton and silk, portions of 

 insects, especially the scales of the common clothes- 

 moth, starch granules, pollen grains, fragments of 

 wood, and animal and vegetable germs, are among 



* See for example " How to Work with the Microscope," 4th edition, 

 p, 195, Plate XLIV. 



