358 POPULAR FALLACIES. 



moment, wc perish ; and so constant is the necessity of the blood for contact 

 with the atmosphere, that every drop in the body is exposed to the air 

 through the medium of the lungs every two minutes and a half of our ex- 

 istence. 



Whatever may be the impurity of the out-door air of any locality, the 

 indoor air of that locality is still more impure, because of the dust and de- 

 caying and odoriferous matters which are found in all dwellings. Besides, 

 how can the in-door air be more healthy than the out-door air, other things 

 being equal, when the dwelling is supplied with air from without? 



To this ver}^ general law there is one exception, which it is of the 

 highest importance to note. When the days are hot, and the nights cool, 

 there are periods ef time within each twenty-four hours, when it is safest to 

 be in-doors, with doors and windows closed ; that is to say, for the hour or 

 two including sunrise and sunset, because about sunset the air cools, and the 

 vapors which the heats of the day have caused to ascend far above us, con- 

 dense and settle near the surface of the earth, so as to be breathed by the 

 inhabitants ; as the night grows colder these vapors sink lower, and are 

 within a foot or two of the earth, so they are not breathed. As the sun rises, 

 these same vapors are warmed, and begin to ascend, to be breathed again, 

 but as the air becomes warmer, they are carried so far above our heads as to 

 innocuous. Thus it is that the old citizens of Charleston, S. C, remember, 

 that while it was considered important to live in the country during the 

 summer, the common observation of the people originated the custom of rid- 

 ing into town, not in the cool of the evening or of the morning, but in the 

 middle of the day. They did not understand the philosophy, but they ob- 

 served the fact that those who came to the city at mid-day remained well, 

 while those who did so early or late suffered from it. 



All strangers at Eome are cautioned not to cross the Pontine marshes 

 after the heat of the day is over- Sixteen of a ship's crew, touching at one 

 of the West India islands, slept on shore several nights, and thirteen of them 

 died of yellow fever in a few days, while of two hundred and eighty, who 

 were freel}^ ashore during the day, not a single case of illness occurred. The 

 marshes above named are crossed in six or eight hours, and many travelers 

 who do it in the night are attacked with mortal fevers. This does, at first 

 sight, seem to indicate that night air is unwholesome, at least in the locali- 

 ties of virulent malarias, but there is no direct proof that the air about sun- 

 rise and sunset is not that which is productive of the mischief. 



For the sake of eliciting the observations of intelligent men, we present 

 our theory on this subject. 



A person might cross these marshes with impunity, who would set out 

 on his journey an hour or two after sundown, and finish it an hour or two 

 before sun-up, especially if he began that journey on a hearty meal, because, 

 in this way, he would be traveling in the cool of the night, which coolness 

 keeps the malaria so near the surface of the earth as to prevent its being 

 breathed to a hurtful extent. 



