Popular Science Monthly/Volume 48/February 1896/Expired Air and Ventilation


THE following are substantially the conclusions reached by Drs. J. S. Billings, S. Weir Mitchell, and D. H. Bergey regarding the composition of expired air and its effects upon animal life, which are published in the Smithsonian Contributions. These contradictions of certain accepted views are important and likely to give rise to discussion.

There is no peculiar organic matter which is poisonous to animals (excluding man) in the air expired by healthy mice, sparrows, rabbits, guinea-pigs, or men. The injurious effects of such air appeared to be due entirely to the diminution of oxygen or the increase of carbonic acid, or to a combination of these two factors. It is very improbable that the minute quantity of organic matter contained in the air expired from human lungs has any deleterious influence upon men who inhale it in ordinary rooms. In ordinary quiet respiration no bacteria are contained in the expired air. In the act of coughing or sneezing such organisms may be thrown out. The minute quantity of ammonia, or of combined nitrogen, or other oxidizable matters found in the condensed moisture of human breath appears to be largely due to products of the decomposition of organic matter which is constantly going on in the mouth and pharynx. The air in an inhabited room, such as a hospital ward, in which experiments were made, is contaminated from many sources besides the expired air of the occupants, and the most important of these contaminations are in the form of minute particles or dusts. The experiments on the air of the hospital ward showed that in this dust there were micro-organisms, including some of the bacteria which produce inflammation and suppuration, and it is probable that these were the only really dangerous elements in this air. The results of experiments, in which animals were compelled to breathe air vitiated by the products of either their own respiration or by those of other animals, make it improbable that there is any peculiar volatile poisonous matter in the air expired by healthy men and animals other than carbonic acid. The effects of reduction of oxygen and increase of carbonic acid, to a certain degree, appear to be the same in artificial mixtures of these gases as in air in which the change in their proportions has been produced by respiration. An excessively high or low temperature has a decided effect upon the production of asphyxia by diminution of oxygen and increase of carbonic acid. At high temperatures the respiratory centers are affected, where evaporation from the skin and mucous surfaces is checked by the air being saturated with moisture; at low temperatures the consumption of oxygen increases and the demand for it becomes more urgent. The proportion of increase of carbonic acid and of diminution of oxygen which has been found to exist in badly ventilated churches, schools, theaters, or barracks is not sufficiently great to account for the discomfort which such conditions produce in many persons, and there is no evidence to show that such an amount of change in the normal proportion of these gases has any influence upon the increase of death-rates which statistical evidence has shown to exist among persons living in crowded and unventilated rooms. It has been well established by observation and statistics that tuberculosis and pneumonia are the diseases most prevalent among persons living and working in unventilated rooms. But consumption and pneumonia are caused by specific bacteria, which for the most part gain access to the air passages by adhering to particles of dust which are inhaled, and it is probable that the greater liability to these diseases of persons living in crowded and unventilated rooms is to a large extent due to the special liability of such rooms to become infected with the germs of these diseases.

The discomfort produced by crowded, ill-ventilated rooms in persons not accustomed to them is not due to the excess of carbonic acid, nor to bacteria, nor in most cases to dusts of any kind. The two great causes of such discomfort, though not the only ones, are excessive temperature and unpleasant odors. The cause of the unpleasant, musty odor which is perceptible to most persons on passing from the outer air into a crowded, unventilated room is unknown; it may, in part, be due to volatile products of decomposition contained in the expired air of persons having decayed teeth, foul mouths, or certain disorders of the digestive apparatus, and it is due in part to volatile fatty acids given off with, or produced from, the excretions of the skin. The results of this investigation, taken in connection with the results of other recent researches, indicate that some of the theories upon which modern systems of ventilation are based are either without foundation or doubtful, and that the problem of securing comfort and health in inhabited rooms requires the consideration of the best methods of preventing or disposing of dusts of various kinds, of properly regulating temperature and moisture, and of preventing the entrance of poisonous gases, like carbonic oxide derived from heating and lighting apparatus, rather than upon simply diluting the air to a certain standard of proportion of carbonic acid present.

It would be unwise, however, to conclude from the facts given in this report that the standards of air supply for the ventilation of inhabited rooms, which are based on the results of Pettenkofer's work, are too large.