242 president's address — section i. 



chief is rubbed between the hands, or if clothes are brushed, the finer 

 dust which is created will be found at a height of 3ft. from the ground 

 after an hour in a still atmosphere. 



The next point that may be considered is the possibility of air- 

 borne bacteria reaching the lungs. Experimental work has proved 

 that, although the majority of the bacteria inspired with the air are 

 deposited on the mucous membranes of the nose, mouth, windpipe, &c., 

 where certain species give rise to throat and other troubles, yet some 

 reach the lungs, where they can be detected. When animals are 

 subjected to an artificially infected atmosphere, the bacteria are found 

 in the finest bronchi and alveoli of the lungs (13, 14). According to 

 Selter (33) a deep inspiration will carry spray droplets from the mucous 

 membranes of the mouth into the lungs. Experiments such as these 

 have to be quickly done, or the microbes may be bacteriolysed, phago- 

 cytosed, or conveyed by the mobile leucocytes to a distant tissue. 

 Even when soot or cinnabar laden air is used the particles can be 

 detected in the bronchial glands, and the inhalation of anthrax spores 

 has resulted in death. (10) 



It is, therefore, evident that bacteria in the air, whether contained 

 in fine spray droplets or in dust, are deposited on the membranes 

 leading to the lungs, and, obtaining access to the lungs themselves, 

 may penetrate to the most remote parts, where a disturbance may be 

 set up. (15) 



Having seen the possibilities of air-infection, let us look at the other 

 side of the question, and see what may occur while the bacteria are 

 suspended in the air or are resting upon a solid surface. The vitahty 

 of the micro-organisms under such conditions has been extensively 

 investigated, chiefly on account of the importance of the matter. 

 The experiments have shown that they are destroyed with greater or 

 less rapidity. Conditions will naturally vary, and a close concordance 

 cannot be expected between the results of the various investigators. 

 Still, if we consider the conclusions generally, we will obtain much useful 

 information. Some bacteria are delicate, and are easily influenced by 

 adverse conditions, compared with other hardier species. Furthermore, 

 the substance upon which they rest, or in which they are contained, has 

 a certain amount of influence. The subject is, therefore, complicated. 



When contained in spray and resting upon glass and freely exposed 

 to the air, the existence of the bacterium depends upon its nature. For 

 example, in diffused daylight the comparatively delicate typhoid 

 bacterium perishes in 24 hours, while the hardier pyogenic micrococci 

 live for 18 days ; the diphtheria micro-organism dies in two days. In 

 the dark, but under the same conditions, Bac. diphtherice may live for 

 five days, the staphylococci for 35 days, and the streptococci for 45 

 days. When the spray droplets fall upon dust the bacteria perish in 

 a much shorter time. Bad. typhi, for example, dies in from six to nine 

 hours in dust exposed to diffused daylight and in 18 hours in the dark.(8). 



When clothes or dust have been infected, the bacteria either lie 

 upon the surface or in the interior of the cloth fibres and dust particles. 

 In the former we have a condition similar to that which can be obtained 



