46 



THE JOURNA.Iv OF PHARMACOLOGY. 



lo. JVood Fibers. — B)^ this name is understood fibers obtained from wood 

 by mechanical means. In wood fibers, therefore, are found all of the ele- 

 ments of wood. Wood-fibers are not only readily recognizable microscop- 

 ically but their origin can usually be ascertained with definiteness. 



For the fabrication of wood-fibers soft varieties of wood are commonly 

 employed such as pine, spruce, fir, aspen, linden, and willow. 



The wood-fibers obtained from evergreens are characterized by being 

 composed of tracheids possessing large bordered pores. These are usually 

 flat, and by the grinding process, become more or less torn, and have blunt 

 broad ends ; they have relatively thin walls (Fig. 7). 



Fig. -. Tracheids and Medullary rays of 

 White Fir. 



Fig. 8. Spruce Tracheids with medullary rays 

 and characteristic Border Pores. 



The wood-fibers of foliage trees do not possess these characteristic trach- 

 eids, but in their places are found numerous short and broad vessel-frag- 

 ments which are thickly covered with small flattened bordered pores. 

 Besides these there are thin fibers (libriform or wood-fibers) which, in the 

 case of the mentioned soft woods, are but little thickened. 



The tracheids do not afford much clue as to which variety of evergreen 

 is used, for they are all much alike in structure. On the contrary, however, 

 the medullary ray cells which occur abundantly in all wood pulps (wood- 

 fibers) differ very much in the particular evergreen trees. Here are briefly 

 given the most important characters by which they may be distinguished 

 (Figs. 7, 8, 9). The medullary ray cells appear in wood-fibers mostly 

 in parallel rows of brick-shaped cells. If all of the cells are provided with 

 simple, roundish pores, the fiber in question is pine wood. If besides these 

 simple, porous medullary cells are also found some which exhibit small, 

 bordered pores, it is probably spruce wood (Fig. 8). If, however, a por- 

 tion of the medullary cells have large and striking indentations reaching 

 far into the lumen (in which small bordered pores may be seen), while the 

 other portion shows a row of large and apparently roundish quadrangular 



