322 THE POPULAR SCIENCE MONTHLY 



anthrax and suppuration. The mere fact that such germs have at times 

 been found, however, is of little significance in the matter of possible 

 aerial infection. They never occur in any considerable numbers, and 

 considerable numbers of germs are usually necessary to produce a dis- 

 ease. It is known that many bacteria on being cast out into the air 

 from an infected source lose their virulence in the process of drying 

 and soon die. Evidence that disease germs pass through the air from 

 room to room of a house or from a hospital to its immediate surround- 

 ings always breaks down when examined critically. It is indeed not 

 rare now to treat cases of different infectious diseases within 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 microbes 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, sneez- 

 ing or forcible speaking. In this manner infection may, and at times 

 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 to us 

 through the medium of the air — aerial infection in the most of those 

 diseases with which we are familiar is, in the authoritative words of 

 Chapin, " under ordinary conditions of home and hospital a negligible 

 factor." Avoid all forms of physical contact with disease germs or 

 germ-laden articles; keep hands and dishes clean; beware of infected 

 food and water ; if you can detect him shun the bacteria-carrier, he who 

 unwittingly carries within his body the germs without the disease and 

 may deposit them where subsequent physical contact is possible; but 

 do not be tormented any longer by the unnecessary specter of germ- 

 laden air. 



I might add a few words concerning sewer gas. Sewer gas consists 

 simply of air containing volatile substances which are given off by 

 the decomposing organic matters that occur in sewage. There is noth- 

 ing mysterious about the components of sewer gas except in the minds 

 of those who stand in dire dread of it. It may contain carbon dioxide, 

 the ill-smelling hydrogen sulphide and ammonium sulphide, marsh gas, 

 ammonia and certain other gaseous substances — all of these in variable, 

 and, with the possible exception of carbon dioxide, usually small 

 amounts. There is no excessively poisonous gas among them. Bacteria 

 exist abundantly in sewage, but these appear to be given off to the air 

 only when the liquid sewage is mechanically splashed and then only in 

 very small numbers and usually not to great distances. Winslow has 

 made a most careful experimental study of this subject, and has come to 



