Motography (Apr-Dec 1911)

November, 1911. MOTOGRAPHY 221 Some Facts About Ventilation HUMAN beings or other animals in a confined space gradually consume the oxygen present and replace it with oxidation products, of which carbon dioxide is the most typical. Hence it was natural that attention should be fixed primarily upon these points, and it is still the popular belief that a crowded room is deficient in oxygen. Quantitative experiments soon showed, however, that these particular dangers were not of practical importance. The victims of the "black hole" of Calcutta, and of the underground prison at Austerlitz, and the unfortunate passengers who were imprisoned beneath the hatches of the ship Londonderry did actually perish from oxygen starvation; and the same thing happens now and again to miners and to sewermen who venture into a clogged manhole or other confined space, filled with inert gases, and there are asphyxiated. Nothing of this sort can, however, happen in an ordinary room or under normal conditions of occupancy. The oxygen in the air must be reduced from 21 per cent to 15 per cent and the carbon dioxide increased from .04 per cent to 3 per cent before any marked physiological effect is manifest. These values are never remotely approached in what we consider an ordinary ill-ventilated room. REBREATHED AIR IS NOT DANGEROUS. The next important theory that took possession of sanitarians and pseudo-sanitarians depended on the assumption that in addition to its more obvious constituents rebreathed air contained a mysterious organic emanation of poisonous nature, which was called "crowd poison" or "morbific matter." This theory rested primarily on the observed fact that crowded rooms have a foul, stale odor, and in some experiments of Brown-Sequard's which were later shown to be erroneous. It is certainly true that to anyone entering an ill-ventilated room from purer outside air, a marked and characteristic odor is apparent. This is undoubtedly due not to any organic matter discharged from the lungs but to the emanations from clothing, bodies and teeth. It is usually not particularly noticeable to those who have been within the room during its gradual increase. There is no evidence that it exerts any harmful physiological effects and some evidence that it does not. Careful investigations made by physiologists of the highest standing have wholly failed to demonstrate any unfavorable effects from rebreathed air with all that it contains, provided only, that the temperature be kept at a proper level. Benedict and Milner observed seventeen different subjects kept for periods varying from two hours to thirteen days in a small chamber with a capacity of 189 cubic feet in which the air was changed only slowly, while the temperature was kept down from the outside. The amount of carbon dioxide Avas usually over thirty-five parts (or eight to nine times the normal) and during the daytime when the subject was active, over 100 parts, and at one time reached 240 parts ; and all the "morbific matter" or other deleterious entities which usually accompany carbon dioxide must have been present in corresponding proportion. Yet there was no discomfort whatever, and *From an Article in the School Board Journal. no detectable disturbance of normal physiological functioning as long as the chamber was kept cool. Dr. Leonard Hill has recently placed eight men in a closed chamber of 106 cubic feet capacity. At the end of half an hour the wet bulb temperature in the chamber had risen to 85 degrees F., the faces of the subjects were congested and they experienced great discomfort ; but their feelings were at once relieved, without changing the air at all, by stirring it up and cooling their bodies by the motion of electric fans within the chamber. From these experiments, and from similar ones carried out by Fluegge and others, we may safely conclude that danger from the chemical constituents of ordinary rebreathed air is in the light of present knowledge so slight as to be negligible to all intents and purposes. DISEASE BACTERIA IN AIR. Another point which has received more than its due share of popular attention is the possibility of the spread of disease bacteria in air. It is common for the "yellow sanitarian," if one may coin a term, to expose plates in a crowded room and show that a great many bacteria fall upon them, and then to call on us all to share his horror. I have been informed that at one large New England college the member of the faculty responsible for hygiene and sanitation is accustomed to order the disinfection of any classroom which shows a count beyond a certain limit. As a matter of fact, however, the bacteria in air are in overwhelming proportion, good, harmless saprophytic organisms. It is true that tubercle bacilli and some other pathogenic germs have occasionally been found in dust and dusty air, but rarely and in small numbers. While many disease germs are not immediately killed by drying, we may be sure from our knowledge of the general behavior of parasitic organisms outside the body that the percentage reduction in living virulent germs is rapid. From a bacteriological standpoint it is clear that air bacteria must be insignificant in their effects, compared from a quantitative standpoint, with the infection carried from person to person by many direct means. Dr. Chapin, in his admirable book on "The Sources and Modes of Infection," has shown that clinical and epidemiological evidence "'points in the same direction — that the common diseases are" not easily transmissible through the air. . , It is, of course, true that in coughing, sneezing or loud speaking a spray of often richly infected droplets is discharged, and Dr. W. A. Evans of Chicago has drawn a picture of the danger from an incipient sick person who runs for a car and just makes the crowded back platform, puffing and coughing in the faces of his neighbors. This is dangerous enough, but it is not air infection. The mouth spray is a local rain which drops quickly to the ground, not a general pollution of the atmosphere. It could not be detected by any analytical standards, and could not be remedied by ventilation. It is a kind of direct contact rather than a problem of air pollution. HIGH HUMIDITY HARMFUL. The really important factors which make for health or disease in the atmosphere are physical rather