84 
SOURCES OF ANIMAL HEAT AND MOTION. 
3. The source of vital force in the vegetable kingdom is 
found in the sun’s rays; whilst the organ of all vital pheno¬ 
mena in animals is found in the mutual action of oxygen and 
the elements of their food. 
4. All truly vital operations of the animal, as well as the 
vegetable organism, are performed by the agency of untrans¬ 
formed cells: disintegration of the cell is one essential condi¬ 
tion or source of its action, and the amount of vital action 
which each cell can perform is limited; hence it is now 
generally held that the essential organic form, the acting 
living organism, is the cell—the complex organism only 
supply the conditions requisite for the vital operations. For 
example, the liver and kidne} T s, by the peculiar arrangement 
of their tissues, simply supply the conditions by which the 
cells perform their functions. 
The manifestations of the vital force are dependent on a 
fixed composition of the substances of the living tissues by 
which they act, which enables these to resist the changes 
that external agencies tend to produce. The vital force does 
not act, like the magnetic force, at infinite distances, but, like 
chemical force, it is active only in the case of immediate 
contact; its manifestations are also dependent on a certain 
temperature. 
Abstraction of heat, or expenditure of force of living parts, 
weaken their resistance to the chemical action of oxygen; 
thus, if we lower the temperature of the skin, oxygen instantly 
decomposes the fatty matters of certain cells, converting 
them into carbonic acid and water, setting their vital force at 
liberty as radiant heat. Each cell also performs a definite 
function, generates force of a definite character; the cells of 
the brain generate mind (brain-force), those of the muscles, 
motor power (muscle-force.) 
All phenomena of vitality are phenomena of motion. If I 
may be permitted to imagine a starting point of motion, and 
assume that a thought excited by light or sound (phenomena 
of motion) causes a change in certain cells of the brain, 
which enables oxygen to decompose their contents and set 
free a force (brain-force), this passes as a wave along the 
spinal cord to special conductors, the nerves; this nerve-force 
excites a change in the muscle-cells, and oxygen decom¬ 
poses them, producing the phenomena of muscular motion 
(muscle-force); the cells lose their vital properties, their 
character of life, and separate from the living part; but, to 
continue, the muscles act upon the tendons and bones, 
imparting motion to the limbs, and liberating the force as 
heat, which now takes its leave of the living body, and 
returns to the “outer world” from whence it came. 
