BACTERIA IN THE AIR 103 



turbance. The position is precisely analogous to the 

 germ-free sewer air as established by Messrs. Laws and An- 

 drewes for the London County Council. The popular idea 

 that infection can be " given off by the breath " is contrary 

 to the laws of organismal pollution of air. The required 

 conditions are not fulfilled, and such breath infection must 

 be of extremely rare occurrence. The air can only be infec- 

 tive when filled with organisms arising from dried surfaces. 



The other series of investigations were conducted by Drs. 

 Hewlett and St. Clair Thompson, and dealt with the fate 

 of micro-organisms in inspired air and micro-organisms 

 in the healthy nose. They estimated that from 1500 

 to 14,000 bacteria were inspired every hour. Yet, as we 

 have pointed out, expired air contains practically none at 

 all. It is clear, then, that the inspired bacteria are de- 

 tained somewhere. Lister has pointed out, from observ- 

 ation on a pneumo-thorax caused by a wound of the lung 

 by a fractured rib, that bacteria are arrested before they 

 reach the air-cells of the lung; hence it is at some inter- 

 mediate stage that they are detained. Hewlett and Thom- 

 son examined the mucus from the wall of the trachea, and 

 found it germ-free. It was only when they reached the 

 mucous membrane and moist vestibules and vibrissae of the 

 nose that they found bacteria. Here they were present in 

 abundance. The ciliated epithelium, the moist mucus, and 

 the bactericidal influence of the wandering or " phagocyte " 

 cells probably all contribute to their final removal. 1 



There can be no doubt that the large number of bacteria 

 present in the moist surfaces of the mouth is the cause of a 

 variety of ailments, and under certain conditions of ill- 

 health organisms may through this channel infect the whole 



1 Hewlett and Thomson graphically demonstrated the bactericidal power of 

 the nasal mucous membrane by noting the early removal of Bacillus prodigiosus, 

 which had been purposely placed on the healthy Schneiderian membrane of the 

 nose. 



