The amount of danger to human health incurred through the presence of disease germs in the atmosphere has been the subject of much controversy. The present tendency is to regard this danger as very slight, under ordinary conditions. Thus, Dr. F. S. Lee writes:
“Evidence that disease germs pass through the air from room to room of a house or from a hospital to its immediate surroundings always breaks down when examined critically. It is indeed not rare now to treat cases of different infectious diseases in the same hospital ward. The one place of possible danger is in the immediate vicinity of a person suffering from a disease affecting the air passages, the mouth, throat, or lungs, such as a ‘cold’ or tuberculosis. Such a person may give out the characteristic microbe for a distance of a few feet from his body, not in quiet expiration, for simple expired air is sterile, but attached to droplets that may be expelled in coughing, sneezing, or forcible speaking. In this manner infection may, and probably does, occur, the evidence being perhaps strongest in the case of tuberculosis. But apart from this source there appears to be little danger of contracting an infectious disease from germs that float in the air.”
In regard to sewer gas, which still inspires so much dread in the popular mind, Dr. Lee says:
“Workmen in sewers are notoriously strong, vigorous, healthy men, with a low death rate among them. The specter of an invisible monster entering our homes surreptitiously from our plumbing pipes and sapping our lives and the lives of our children must be laid aside; we need no longer leave saucers of so-called ‘chlorides’ standing about our floors to neutralize in an impossible manner mysterious effluvia that do not exist; and when we return to our town houses in the autumn we may enter them with no fears that we are risking our lives by coming into a toxic, germ-infected, sewer gas-laden, deadly atmosphere.”
Present-day knowledge on the subject of infectious diseases discredits many ideas that once prevailed with regard to the effects of tropical climates on health. The remarkable results accomplished by vigorous sanitary measures in such places as Havana, the Isthmus of Panama and Guayaquil have aroused hopes—perhaps too sanguine—that eventually all parts of the tropics will be made healthful for the white race. In the Canal Zone the death rate of the large population of American men, women, and children is not higher than prevails in many cities of the United States; whereas, a generation ago, when the French were at work on the canal, the “climate” of this region was regarded as one of the most unhealthful in the world. Some authorities go so far as to assert that the deterioration in the general health and efficiency of white people in the tropics, so far as it actually occurs, is due entirely to preventable diseases. It would seem more rational, however, to assume that there are climates both in and out of the tropics which, on account of their heat, humidity, and other purely physical factors, are not so suitable for habitation for any race of humanity as others. How far acclimatization can go toward offsetting the effects of these atmospheric conditions is problematical.
The changes in the barometer that occur from day to day in regions where these changes are most pronounced are, on an average, not greater than those encountered in going from the bottom to the top of a good-sized hill, and are probably not directly of physiological importance. Certain European investigators, however, ascribe pathological effects to the minute and rapid barometric fluctuations—too small to be detected with an ordinary barometer—that occur, for example, when the foehn wind is blowing. Whether this is the cause, or a contributory cause, of “foehn-sickness,” of which one hears in Switzerland, is still uncertain.
The physiological effects of a rarefied atmosphere, as experienced in mountain climbing, ballooning, and aviation, are not yet well understood, despite the large amount of study that has been devoted to this subject. Recent views are thus summarized by Rosenau:
“The symptoms produced by a marked diminution in atmospheric pressure vary with circumstances. The effects are increased by cold, active muscular exertion, or improper clothing. The noticeable symptoms are increased rapidity of respiration and acceleration of the circulation, noises in the head and dizziness, impairment of the senses of sight, hearing, and touch, dullness of the intellectual faculties, and a strong desire to sleep. Sudden changes to a rarefied atmosphere cause syncope, weakness, dyspnœa, dizziness, and nausea. These threatening symptoms go by the name of ‘mountain sickness,’ Bert and Journet believe this condition is due to lack of oxygen, and the symptoms may, in fact, be relieved by adding oxygen to the air inspired. Kronecker concludes that mountain sickness is caused by a congestion of the lungs, impeding the flow of blood through them. Mosso and his followers attribute the physical disturbances of a reduced atmospheric pressure to the fact that the blood loses carbon dioxide more quickly than it loses oxygen, and they ascribe mountain sickness to this decrease of carbon dioxide in the blood. Cohnheim believes there is a concentration of the blood at high altitudes; in fact, insignificant increases have been found by competent observers.”
Divers and workers in caissons are subjected to high barometric pressure, amounting, at the maximum, to about 4½ atmospheres. According to Rosenau:
“The physiological effects of an increased atmospheric pressure are mainly due to an increase in the amount of atmospheric gases (especially nitrogen) which are taken up by the blood, and also to an increase in the chemical absorption of oxygen by the blood. The serious consequences usually result from too rapid decompression. As the pressure is released gas bubbles form. Gradual decompression gives a chance for the gas to escape from the lungs and be expelled without the production of bubbles.”