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.

Q. _How does INHALING AIR RAPIDLY make the body feel WARM?_

A. As the combustion of the blood is _more rapid_, (in consequence of the introduction _of more oxygen from the air_), therefore _the blood is more heated_, and every part of the body is warmer also.

Q. _Why does HARD WORK produce HUNGER?_

A. Because it produces _quicker respiration_; by which means a _larger amount of oxygen is introduced into the lungs_, and the _capillary combustion increased_. Hunger _is the notice_ (given by our body) to remind us, _that our food-fuel must be replenished_.

Q. _Why does SINGING make us HUNGRY?_

A. Singing _increases respiration_; and as _more oxygen_ is introduced into the lungs, _our food-fuel is more rapidly consumed_.

Q. _Why does READING ALOUD make us feel HUNGRY?_

A. Reading aloud _increases respiration_; and as _more oxygen_ is introduced into the lungs, _our food-fuel is more rapidly consumed_.

Q. _Why do we feel MORE HUNGRY in the DAY-TIME than in the NIGHT-TIME?_

A. As we _breathe more slowly during sleep_, therefore, less _oxygen_ is introduced into the lungs _to consume our food-fuel_.

Q. _Why do we need WARMER CLOTHING by NIGHT than by DAY?_

A. 1st--Because the _night is generally colder_ than the day.

2ndly--As our _respiration is slower_, our _animal combustion is slower also_; in consequence of which, _our bodies are more cold_.

Q. _Why do we PERSPIRE when very HOT?_

A. The pores of the body are _like the safety valves of a steam-engine_; when the heat of the body is too great, the combustible gas and grease _flow out in perspiration_, instead of _burning in the blood_.

Q. _Why do persons feel LAZY and averse to exercise, when they are HALF-STARVED or ILL-FED?_

A. _Animal food_ contains great nourishment, and produces a desire for _active occupations_; but when the body is not supplied with strong food, this desire for muscular action _ceases_, and the person grows slothful.

Q. _Why have persons, who follow HARD OUT-OF-DOORS OCCUPATIONS, more APPETITE than those who are engaged in SEDENTARY pursuits?_

A. Hard bodily labour in the open air _causes much oxygen to be conveyed into the lungs by inspiration_; the combustion of the food is carried on quickly; _animal heat increased_; and need for nutritious food more quickly indicated _by craving hunger_.

Q. _Why have persons who follow SEDENTARY PURSUITS less APPETITE than ploughmen and masons?_

A. 1st--The air they inhale _is not so pure_, because its oxygen is partly exhausted: and

2ndly--Their respiration is neither _so quick nor strong_, and therefore the combustion of their food is carried on more slowly.

Q. _Why do we like strong MEAT and GREASY food when the WEATHER is very COLD?_

A. Strong meat and grease contain large portions of _hydrogen_, which (when burned in the blood) produce a larger amount of heat than any other kind of food.

Q. _Why do persons EAT MORE food in COLD weather, than in hot?_

A. In _cold_ weather the body requires more fuel _to keep up the same amount of animal heat_; and as we _put more coals on a fire on a cold day_ to keep our _room warm_, so we _eat more food on a cold day_ to keep our _body warm_.

Q. _Why does COLD produce HUNGER?_

A. 1st--The air contains more _oxygen_ in cold weather; and as _fires burn fiercer_, so _animal combustion is more rapid_: and

2ndly--We are more _active_ in cold weather; and increased respiration acts _like a pair of bellows_ on the capillary combustion.

Q. _Why does rapid DIGESTION produce a craving APPETITE?_

A. This is a wise providence to _keep our bodies in health_; in order that the _body itself_ may not be consumed, it gives notice (by hunger) that the _capillary fires need replenishing_.

Q. _Why do we feel a desire for ACTIVITY in cold weather?_

A. 1st--Because activity increases the warmth of the body, _by fanning the combustion of the blood_: and

2ndly--The _strong food_ we eat creates a desire for muscular exertion.

Q. _Why are the Esquimeaux so passionately fond of TRAIN OIL and WHALE BLUBBER?_

A. Oil and blubber contain a very _large amount of hydrogen_, which is exceedingly combustible; and as these people live in climates of intense cold, the heat of their bodies is increased by the _greasy nature of their food_.

Q. _Why do we feel a dislike to strong meat and greasy foods in very hot weather?_

A. Strong meat and grease contain so much _hydrogen_, that they would make us _intensely hot_; and therefore we refuse them in hot weather.

Q. _Why do we like fruits and vegetables so very much in hot weather?_

A. Fruits and vegetables contain _less carbon_ than meat, and therefore produce _less blood_: instead of blood, _they combine into water_ as they are digested, and keep the body cool.

Q. _Why do people say that FRUITS and VEGETABLES COOL the BLOOD?_

A. 1st--Because they _deprive the blood of carbon_, which is the chief cause of animal heat: and

2ndly--These gases coalesce into _water_, which greatly tempers the animal heat.

Q. _Why do we feel LAZY and averse to activity in very HOT WEATHER?_

A. 1st--Because muscular activity would increase the heat of the body, by _quickening the respiration_: and

2ndly--The food we eat in hot weather, _not being greasy_, naturally abates our desire for bodily activity.

Q. _Why do the inhabitants of tropical countries live chiefly upon rice and fruit?_

A. Rice and fruit by digestion _are mainly converted into water_, and (by cooling the blood) prevent the tropical heat from feeling so oppressive.

Q. _Why are POOR PEOPLE generally AVERSE to CLEANLINESS?_

A. 1st--_Cleanliness increases hunger_; and as poor people are generally _ill-fed_, they are averse to cleanliness.

2ndly--_Dirt is warm_, (thus pigs who love _warmth_, are fond of _dirt_); and as poor people are generally _ill-clad_, they like the _warmth of dirt_.

Q. _Why are POOR PEOPLE generally AVERSE to VENTILATION?_

A. 1st--Because ventilation _increases the oxygen of the air_,--the _combustion of food_,--and the _cravings of appetite_: and

2ndly--Ventilation _cools the air of our rooms_: poor people, therefore, (who are generally ill-clad) love the _warmth_ of an ill-ventilated apartment.

Q. _Why does FLANNEL, &c. make us WARM?_

A. Flannel and warm clothing do not _make_ us warm, but merely _prevent the body from becoming cold_.

Q. _How does flannel, &c. prevent the body from becoming cold?_

A. Flannel (being a bad conductor) will _neither carry off the heat of the body into the cold air_, nor suffer the cold of the air _to come into contact with our warm bodies_; and thus it is that flannel clothing keeps us warm.

Q. _Why are FROGS and FISHES COLD-BLOODED animals?_

A. Because they consume _so little air_; and without a plentiful supply of air, combustion is so slow, that very little animal heat is evolved.

Q. _Why is a DEAD BODY COLD?_

A. Air is no longer conveyed to the lungs after respiration has ceased; and, therefore, animal heat _is no longer evolved by combustion_.