More than that of any other artists, perhaps, the oeuvre of the rock group Crowded House is rich in references to weather. The variability of our climate, for example, is admirably summed up as follows: The sun shines on the black clouds over the domain; Even when you're feeling warm The temperature could drop away, Like four seasons in one day.
Equally perspicacious is the group's observation that Everywhere you go, you always take the weather with you.
Indeed, such was the importance to them of this concept that they made it, not only the title of a song, but also - with the phrase repeated several dozen times - its entire lyric. Nowhere, moreover, is their assertion more correct than when one enters the domain suggested by their very name, a Crowded House.
Leaving aside such extraneous factors as cigar smoke, five different changes can be identified as taking place in the air inside a crowded house. Two of these are obvious: by their collective breathing, the assembled crowd reduces the oxygen content of the air, and increases the proportion of carbon dioxide it contains. In addition, body heat from the assembled humans increases temperature inside the rooms, and the moisture of their exhalations brings about a rise in the humidity. Indeed, any discomfort we may suffer in a stuffy room is rarely due to lack of oxygen, or to the higher proportion of carbon dioxide in the air. In a very crowded and poorly ventilated space, the oxygen content of the air will rarely drop below 20 per cent, compared to the normal concentration of about 21 per cent; carbon dioxide, in similar circumstances, may rise more dramatically, from 0.03 to, say, 0.5 per cent.
In both cases, however, the changes fall far short of those known to produce harmful, or even noticeable, physiological effects: the human breathing apparatus can easily accommodate itself to wide variations in the external mix by means of very slight and automatic changes in the rate and depth of respiration. The fifth and final process, however, is more subtle in its modus agendi if not in its effect. The reaction of oxygen in the air with certain substances exuded by the body, or already present on the surface of the skin or articles of clothing, releases variable amounts of aromatic compounds into the surrounding atmosphere.
These, and the exhaled effects of decomposition in uncared-for mouths, combine to produce the "body odour" that we notice when we enter an unventilated crowded room from the fresher air outside.