
a 
SECT. XIX. PHYSIOLOGY. 171 
other parts, is the cause of the decompositions 
which occur in the alimentary canal. 
cceccxvit. In the stomach, the points of contact 
between the nervous and vascular systems, are 
more numerous than in any other part of the 
alimentary tube; and there, too, decomposition 
is most rapidly effected. 
ecccx1x. Digestion is not, however, confined 
to simple decomposition of substances submitted 
to its vital force; there is likewise a re-union of 
the particles of the decomposed substance into a 
new homogeneous mass, which in its turn under- 
goes successive mutations. The substances decom- 
posed, in all instances contain the ingredients of 
the new product, but require to have their particles 
differently arranged before they can be fitted for 
the various purposes to which they are destined. 
Thus, a piece of muscle may contain all the 
integrant particles necessary for nutrition, at least 
it can assimilate with living parts, but in its solid 
state it cannot pass into the circulating mass of 
fluids to excite the nervous system and supply 
the materials of organization. 
cecccxx. Digestion thus consists of two processes 
—decomposition of aliment, and chylification. 
ccccxxi, Mastication is a preparation of the 
aliment for digestion, by which it is mechanically 
comminuted by the teeth, and lubricated with 
saliva, of which the motion of the lower jaw, 
