80 BACTERIA IN THE AIR 



it is concluded that "in ordinary quiet respiration no bacteria 

 epithelial scabs or particles of dead tissue are contained in the 

 expired air. In the act of coughing or sneezing such organisms or 

 particles may probably be thrown out." The mucous membrane 

 lining the cavity of the mouth and respiratory tract is a moist 

 perimeter, from the walls of which no organisms can rise except 

 under molecular disturbance. The popular idea that bacteria can 

 be "given off by the breath" is therefore 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 except in speaking, spitting, sneezing or coughing 

 (Fltigge). Air can only become infective when impregnated with 

 organisms arising from dried surfaces. 



Another series of investigations were conducted by Drs Hewlett 

 and St Glair Thomson, 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 seen, expired air contains practically none 

 at all. It is clear, then, that the inspired bacteria are detained some- 

 where. Lister has pointed out, from observation on a pneumo-thorax 

 caused by a wound of the lung by a fractured rib, that bacteria may 

 be arrested before they reach the air cells of the lung, and other 

 observations confirm this fact, although of course there are several 

 well-known exceptions (e.g. tubercle of the lung). Hence it is at 

 some intermediate stage that they are detained. Hewlett and 

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

 found it germ-free. It was only when they examined the mucous mem- 

 brane and moist vestibules and vibrissae of the nose that (they found 

 bacteria* Here they were present in abundance. The ciliated 

 epithelium, the mucus, and the bactericidal influence of the wandering 

 or " phagocyte " cells, probably all contribute to their final removal.* 



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 body. Dental caries will occur 

 to everyone's mind as a disease probably due in part to bacteria. As 

 a matter of fact, acids (due to acid secretion and acid fermentation) 

 and micro-organisms are two of the chief causes of decay of teeth. 

 Defects in the enamel, inherent or due to injury, retention of debris 

 on and around the teeth, and certain pathological conditions of the 

 secretion of the mouth, are predisposing causes, which afford a 



* 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. 



