A. Because it both _concentrates and reflects the heat of the flame_; in consequence of which, the heat is so greatly increased, _that very little carbon escapes unconsumed_.

CHAPTER VI.

ANIMAL HEAT.

Q. _What is the cause of ANIMAL HEAT?_

A. Animal heat is produced _by the combustion of hydrogen and carbon_ in the capillary veins.

Q. _What are CAPILLARY VEINS?_

A. Veins _as small as hairs_ running _all over the body_; so called from the Latin word "capilla'ris" (_like a hair_).

Q. _Do these CAPILLARY VEINS run all over the human body?_

A. Yes. Whenever blood _flows from a wound_, some _vein_ must be divided; and as you cannot insert a needle into _any part of the body without bringing blood_, therefore these little veins must run _through every part_ of the human frame.

Q. _How do HYDROGEN gas and CARBON get into these very little veins?_

A. The food we eat is _converted into blood_, and blood contains both _hydrogen_ and _carbon_.

Q. _How does COMBUSTION take place in the veins?_

A. The _carbon of the blood_ combines with the _oxygen of the air we breathe_, and forms into _carbonic acid gas_.

Q. _What BECOMES of this CARBONIC ACID GAS formed in the human blood?_

A. Some of it is _thrown off by the breath_; and the rest of it is _absorbed by the blood_, to keep up the animal heat.

Q. _What is the cause of the COMBUSTION of FIRE?_

A. The _carbon of fuel_ unites with the _oxygen of the air_, and forms _carbonic acid gas_.

Q. _What is the cause of the COMBUSTION of a CANDLE or LAMP?_

A. The _carbon of the oil or tallow_ unites with the _oxygen of the air_, and forms _carbonic acid gas_.

Q. _What is the cause of SPONTANEOUS COMBUSTION?_

A. The piled-up goods _ferment from heat and damp_; and (during fermentation) _carbonic acid gas is formed_, as in the two former cases.

Q. _Does the HEAT of the HUMAN BODY arise from the SAME CAUSE as the heat of FIRE?_

A. Yes, precisely. The _carbon of the blood_, combining with the _oxygen of air inhaled_, produces _carbonic acid gas_, which is attended with combustion.

Q. _If animal heat is produced by COMBUSTION, why does not the human body BURN UP like a coal or candle?_

A. It actually does so. Every muscle, nerve, and organ of the body, actually _wastes away like a burning candle_; and (being reduced to air and ashes) is rejected from the system as useless.

Q. _If every bone, muscle, nerve, and organ, is thus consumed by combustion, why is not the BODY entirely CONSUMED?_

A. It would be so, unless the parts destroyed _were perpetually renewed_: but as a lamp will not go out, _so long as it is supplied with fresh oil_; neither will the _body_ be consumed, _so long as it is supplied with sufficient food_.

Q. _When a man is STARVED, what parts of the body go first?_

A. First the _fat_, because it is the most combustible; then the _muscles_; last of all the _brain_; and then the man dies, like a _candle which is burnt out_.

Q. _Why does WANT of sufficient NOURISHMENT often produce MADNESS?_

A. After the _fat and muscles_ of the body have been consumed by animal combustion, the _brain_ is next attacked; and (unless the patient dies) _madness must ensue from starvation_.

Q. _Why does a man SHRINK when STARVED?_

A. A starved man shrinks _just as a fire does_, unless it be supplied with sufficient fuel.

Q. _What is the FUEL of the BODY?_

A. _Food is the fuel of the body_; and the _carbon of the food_ mixing with the _oxygen of the air_, evolves heat in the same way that a fire or candle does.

Q. _Why is EVERY part of the BODY WARM?_

A. As the capillary veins run through every part of the human body, and the combustion of blood _takes place in the capillary veins_, therefore _every part of the body is warm_.

Q. _Why does RUNNING make us WARM?_

A. When we run, _we inhale air more rapidly_; and the rapidity with which we inhale air _fans the combustion of our body_, as a pair of _bellows_ quickens the flame of a common fire.