FRESH AIR 321 



dust is harmless. It is not so, however, with the dusts produced abun- 

 dantly in various trades, such as in the manufacture of cutlery, pottery, 

 porcelain, glass, copper, iron, steel, brass and lead wares, in stone-cut- 

 ting and cotton manufacture. Some of these industrial dusts are poi- 

 sonous; some are mechanically irritating to the walls of our air pas- 

 sages. In dusty occupations such diseases as bronchitis, tuberculosis 

 and pneumonia are unduly prevalent, and there is no doubt that their 

 beginnings lie in local injuries to the lungs produced by the inhaled 

 particles and that these injuries are followed by the lodgment of the 

 specific bacteria. 



Of the bacteria of the air and their relation to disease I must speak 

 at greater length. From the earliest times the belief has existed that 

 bad air is a prolific source of disease. The word "malaria" literally 

 means " bad air," and the disease malaria was the type of those diseases 

 that were supposed to be spread through the atmosphere. In the early 

 days of the germ theory air was regarded as the chief medium of the 

 transmission of disease germs. As one writer graphically put it, dis- 

 ease is " literally borne on the wings of the wind." The great surgeon 

 Lister accepted this notion and conceived the idea of improving surgical 

 technique by maintaining a continual and very fine spray of carbolic 

 acid in the air in the immediate vicinity of the operation. Thus anti- 

 septic surgery arose. Although surgery has now gone far beyond this 

 stage and no longer regards the air as a source of operative infection, 

 the general notion of aerial infection still prevails. But a multitude of 

 facts, gradually accumulated, show that this notion must be revised. It 

 is true that bacteria may be moved through the air, and this may occur 

 under three conditions: when they are freely floating, when they are 

 attached to particles of dust, and when they are contained within the 

 bodies of flying insects. The dissemination of disease germs by insects 

 is a serious fact — the mysterious miasma of malaria lies only within 

 the body of the mosquito, and malaria is still the type, but in a new 

 sense, of certain diseases that are spread through the atmosphere. But 

 there are many reasons for believing that the danger of infection through 

 germs freely floating in air or attached to particles of dust has been 

 much exaggerated. Living organisms, it is true, may be found in the 

 atmosphere of inhabited localities under almost any circumstances. 

 To capture them it is only necessary to expose to the air for a few 

 moments a sterilized plate covered by a layer of nutrient agar on which 

 the floating particles may fall. If the plate be then covered and trans- 

 ferred to a warm place, the organisms will proceed to multiply and de- 

 velop colonies. It is then found that they comprise bacteria and some 

 other microscopic forms. By far the greater number are quite harmless, 

 but pathogenic or disease-producing species do occur. These may in- 

 clude germs of tuberculosis, diphtheria, typhoid fever, dysentery, 



