president's address — SECTION I. 241 



emitted by infected persons, and with Bac. prodigiosus, which is absent 

 in ordinary air, but is, on account of the briUiant red color of its 

 colonies, easy to recognise. (c) 



Gordon (10) detected characteristic salivary bacteria 40ft. in front 

 of and 12ft. behind a man who had spoken energetically for an hour 

 in a still room. This confirmed the experiments made by Fliigge and 

 his pupils with Bac. prodigiosus. That the bacteria ejected by a speaker 

 in a quiet room should reach a distance of 40ft. shows the danger to 

 which an audience might be subjected by a consumptive or other in- 

 fectious person speaking in a small or ordinary room. Even when a 

 handkerchief is held before the mouth to catch the largest particles 

 and deflect the direction of emission, bacteria are still sent outwards, 

 although not to so great a distance. The danger, however, is but 

 little minimised by the interposition of the hand or handkerchief, for 

 a slight air-current may do what the hand was meant to prevent. 

 Experimenting in the open air, Hutchison (11) detected bacteria 

 carried by the wind to places 180yds., and in one case even to 650yds., 

 from the place of origin. Coughing and sneezing send a greater 

 number of spray particles into the air, and although many of them are 

 of comparatively large size, and settle quickly, yet a very large number 

 remain suspended for long intervals. Fliigge found that the finest 

 droplets remained floating for from four to six hours, while Hutchison 

 detected them at the end of eight hours in a still atmosphere. They 

 do not appear to rise, but are continually falling, and, according to 

 Heymann (12), the rate of sedimentation is proportional to the size 

 of the micro-organism. 



We thus see that the finest spray droplets have the power of re- 

 maining suspended in the atmosphere for a comparatively long time, 

 and that air infected by the speaking, coughing, or sneezing of an 

 infectious individual may remain so for from four to eight hours. It 

 is obvious that the only means available for getting rid of the danger 

 in the air is to be found in thorough ventilation. The infected air must 

 be so diluted that there is an infinitely small chance of a microbe being 

 inhaled by a susceptible individual. 



But the infectivity of the larger drops does not end when they 

 leave the air and settle upon the ground, for this term includes carpets, 

 floors, clothes, &c. Carpets and floors are swept and clothes are brushed, 

 with the result that a certain amount of infected fibres or dust is again 

 sent into the atmosphere. The larger and heavier particles soon fall, 

 but the smaller, and especially the fibres," float for a considerable time. 

 When carpets are shaken, none of the dust which is created can be 

 found in 10 minutes higher than a yard from the floor. If a handker- 



(c) ^Vl^en using Bac. prodigiosus, the mouth of the experimenter is rinsed with 

 a suspension of the bacteria before performing the various acts which the experi- 

 ment demands. As a rule, an empty room, such as a lecture hall, is utilised, and 

 plates of nutritive media are distrrbuted at various distances from the investigator, 

 who either speaks, reads, coughs, or sneezes. In dealing with infectious dust, &e., 

 the experiments are made in specially devised boxes or chambers, with all the 

 necessary fi^^tings for blowing the dust and removing the infected media. The 

 experiments with consumptives are also made in special chambers. 



