But what is fermentation?  It is, necessarily, a question of the growth of bacteria and is a process which we may easily watch in our own kitchens.  Bread rises when the yeast-cells have multiplied and acted on the starch of the flour, producing enough gas to raise the whole mass.  Potatoes ferment because bacteria have multiplied within them.  Canned fruit blows up because enough bacteria have developed inside to produce sufficient gas to blow open the can.  Every housewife knows that it takes time for each of these processes.  Bread has to stand several hours before it will rise; potatoes do not ferment under twelve hours, and canned fruit is not considered safe from the fermenting process under three days.  Evidently there is some mistake when a person begins to belch forth “gas” within an hour or two after a meal.  As a matter of fact, it is not gas at all but merely air that is swallowed with the food or that was present in the empty stomach.

When the food enters the stomach it necessarily displaces air, which normally comes out automatically and noiselessly.  But if, through fear or attention, a certain set of muscles contract, the pent-up air may come forth awkwardly and noisily or it may stay imprisoned until we take measures to let it out.  A hearty laugh is as good as anything, but if that cannot be managed, we may have to resort to a cup of hot water which gives the stomach a slap and makes it let go.  Two belches are enough to relieve the pressure.  After that we merely go on swallowing air and letting it out again, a habit both awkward and useless.

If the emotion which ties the muscle-knot is very intense, and the stomach refuses to let go under ordinary measures, the pain may be severe.  But a quantity of hot water or a dose of ipecac is sure to relieve the situation.  If the person is able to give himself a good moral slap and relax his unruly muscles, he reaches the same end by a much pleasanter road.

Some people are fond of the popular remedy of hot water and soda.  Their faith in its efficacy is likely to be increased by the good display of gas which is sure to follow.  As any cook knows, soda and acid always fizz.  The soda is broken up by the hydrochloric acid of the stomach and forms salt and carbon dioxid, a gas.  However, as the avowed aim of the remedy is the relief of gas rather than its manufacture, and as the soda uses up the hydrochloric acid needed in digestion, the practice cannot be recommended as reasonable.

=Gastritis.= I once knew a woman who went to a big city to consult a fashionable doctor.  When she returned she told with great satisfaction that the doctor had pronounced her case gastritis.  “It must be true,” she added, “because I have so much gas on my stomach!” The diagnosis of gastritis used to be very common.  The ending itis means inflammation,—­gastritis, enteritis, colitis, each meaning inflammation of the corresponding organ.  An inflammation implies an irritant.