DAMP SURFACES 79 



and yet retain their virulence. It will be obvious that from these 

 data it is inferred that Groups 1 and 2 are rarely conveyed by the air, 

 whereas Group 3 is frequently so conveyed. Miquel has recently 

 demonstrated that certain soil bacteria or their spores can remain 

 alive in dried dust in hermetically sealed tubes for as long a time as 

 sixteen years. Even at the end of that period such soil inoculated 

 into a guinea-pig produced tetanus. 



The presence of pathogenic bacteria in the air is, of course, a 

 much rarer contamination than the ordinary saprophytes. The 

 tubercle bacillus has been not infrequently isolated from dry dust 

 in consumption hospitals, and in exit ventilating shafts at Brompton 

 the bacillus has been found. From dried sputum, it has, of course, 

 been many times isolated, even after months of desiccation. Indeed, 

 a very large mass of experimental evidence attests the fact that the 

 air in proximity to dried tubercular sputum or discharges may 

 contain the specific bacillus of the disease. The bacillus of diphtheria 

 in the same way, but in a lesser degree, may be isolated from the 

 air, and from the nasal mucous membrane of nurses, attendants, and 

 patients in a ward set apart for the treatment of the disease, and 

 from the throats and nasal mucous membrane of persons who have 

 been in contact with cases of the disease. Delalivesse, examining 

 the air of wards at Lille, found that the contained bacteria varied 

 more or less directly with the amount of floating matter, and 

 depended also upon the vibration set up by persons passing through 

 the ward and the heavy traffic in granite-paved streets adjoining. 

 B. coli, staphylococci, and streptococci, as well as B. tuberculosis, 

 were isolated by this observer. Other observers have found B. coli 

 very rarely present in air (Chick, Andrewes, etc.). 



2. Moisture or Dampness of Surfaces. It is an interesting 

 and important fact that except under special circumstances micro- 

 organisms do not leave moist surfaces, but remain adhering to them. 

 A clear recognition of this fact is essential to a right understanding 

 of the pollution of air by bacteria. They cannot leave the moist 

 surface of fluids either under evaporation or by means of air currents.* 

 Only when there is considerable molecular disturbance, such as 

 splashing, can microbes be transmitted to the surrounding air. 

 This is the reason why sewer gas and all air contained within moist 

 perimeters is almost germ-free, whereas from dry surfaces the least 

 air current is able to raise countless numbers of organisms. 



This principle has been admirably illustrated in investigations 

 made upon expired and inspired air. In a report to the Smithsonian 

 Institute of Washington (1895) upon the composition of expired air, 



* Fliigge has lately attempted to demonstrate that an air current having a 

 velocity of four metres per second can remove bacteria from surfaces of liquids by 

 detaching drops of the liquid itself. 



