PKESIDENt's address — SECTION I. 245 



Tiowever, is not the case ; the great majority of dust particles are 

 sterile. In confirmation of this we have the experiments of Macfadyen 

 and Lunt (20), who found one micro-organism in every 28 million 

 particles of dust in the open air of London, and one mould or microbe 

 in every 184 million motes of an ordinary room. In discussing the 

 comparative poverty of the air as regards bacteria, Fliigge calculated 

 that a man during a life-time of 70 years would inspire 25 millions of 

 these micro-organisms — a quantity which is usually found in half a 

 pint of fresh milk, or in an ounce of milk as we receive it from the 

 dairyman. As to the character of the aerial bacteria, Andrews (21) 

 found that those in the air of London were remarkablv inert in their 

 ■chemical and pathological behaviours, and much the same thing has 

 been said of the micro-organisms in the air of other places. On the 

 other hand, Corcornotti (22), in common with other investigators 

 Tvhom he quotes, found pathogenic bacteria in the air of various places 

 in Sardinia, the most numerous being the pyogenic micrococci ; as 

 would be expected, the more dirty the surroundings the more numerous 

 were the microbes. 



It appears, then, that comparatively few bacteria are inhaled by 

 the individual, and any that are contained in the air, as Moll (23) has 

 pointed out, are deposited upon the mucous membrane of the anterior 

 portion of the nostril, the posterior part being sterile, or nearly so. That 

 many are entrapped follows from Hasslauer's observations (24) upon 

 the bacterial flora of the air- passages of healthy individuals. He 

 found pyogenic cocci in 35 per cent., and pneumococci in 20 per cent, 

 of the cases examined. Kobe (18) found Bac. diphtherice in the throats 

 -of from 8 per cent, to 18 per cent, of persons associated with afiected 

 individuals ; with non-associated persons he detected less than 1 per 

 cent. From the occurrence of so few bacteria in the air, and the 

 rather frequent presence of certain pathogenic microbes in healthy 

 throats, it would appear that once these gain access to the throat 

 they persist there until such time as the vitality of the individual may 

 be lowered, when they assert themselves and produce disease. 



In connection with infection generally, we know that some indi- 

 viduals are more prone to contract disease than others. This condition 

 is referred to as one of individual susceptibility, and means the absence 

 or relative paucity of one or more of the many substances which are 

 included under the general term, immunity bodies. It also includes 

 the absence of that faculty of toleration towards microbes such as we 

 find in the case of a typhoid convalescent, who can retain typhoid 

 bacteria in his body for months or even years. Susceptibility and non- 

 susceptibility towards infection in general are only relative conditions. 

 Other things being equal, one man may be able to overcome, say, ten 

 noxious microbes but not an eleventh, while another may be able to 

 withstand a thousand and no more. An individual susceptible to 

 tuberculosis appears to contract phthisis while living amongst his 

 healthy fellow creatures, and a non-susceptible person succumbs to 

 the repeated infection which obtains in the bed-chamber or living- 

 xoom of a consumptive. There are, however, certain individual 



