WOOD IN GENERAL 249 
iron ones because the latter twist out of shape at high tem- 
perature in a way to wreck the entire structure. (8) Being 
unaffected by wines or other weak acids, and imparting no 
disagreeable flavor, certain woods may be used for casks 
where metal would be objectionable or even poisonous. 
(9) Woods have an organic beauty unrivaled by metals. 
(10) The peculiar elasticity of certain woods render them 
incomparably superior to any metal as material for the res- 
onant parts of violins and similar musical instruments. 
(11) Pieces of wood may be easily and strongly united simply 
by glueing, while metals require the more difficult operation 
of welding or soldering. As against wood it must be said 
(1) that it cannot be melted and cast or rolled; though by 
steaming, rods or sheets may be readily bent into curves of 
small radius; and when reduced to pulp, as we have seen, 
it can be pressed into almost any shape. (2) It shrinks or 
expands with variations of moisture, more than metals do 
under ordinary variations of temperature. (3) It decays 
unless proper precautions are taken to prevent, though under 
water wood lasts longer than steel or iron. (4) It is more 
easily crushed than iron and therefore is not so well suited 
for bearing the greatest weights or for resisting very heavy 
blows. (5) Finally, the greater hardness of many metals 
gives them obvious advantages over wood for sharp imple- 
ments and a large variety of objects that have to stand severe 
wear. A great deal is often gained by combining wood and 
metal because the properties of one so largely complement 
those of the other. 
A piece of wood consists essentially of a mass of extremely 
slender fibers or fibrils, each comparable to a fibril of cotton, 
but firmly cemented together. The valuable qualities of 
woods, and their defects as well, depend in great measure 
upon the character and arrangement of these fibrils and of 
similar parts associated with them. Therefore some knowl- 
edge of the structure of wood helps us to understand its prop- 
erties and to tell one kind of wood from another; and thus 
should lead us to a more intelligent, economical use of the 
material. The fibrous nature of wood is clearly shown by 
its splintery fracture when broken across the grain and by 
