414 Chapter XIII 



defending itself against the invasion of micro-organisms, but the 

 animal organism comes to its aid by sending a permanent army of 

 macrophages which evict from the alveoli, so far as is possible, both 

 micro-organisms and other foreign bodies. Under these conditions, 

 we can readily understand that similar cells which fulfil the same 

 protective function, are also found in the neighbouring bronchial 

 glands. It has long been recognised that the macrophages of 

 these glands are often crammed with various kinds of granules 

 of foreign origin, which have made their way into the lungs with the 

 inspired air. 



Toxic substances can be absorbed by the mucous membrane of 

 the respiratory channels. Roger and Bayeux 1 have shown that no 

 lesion is required in order that diphtheria poison may invade the 

 mucous membrane of the trachea, and so produce typical false mem- 

 branes. The lung, we know, is accessible to gaseous toxic substances ; 

 moreover, its surface readily absorbs fluid poisons. 



The protection of the digestive system is more complex than 

 that of the respiratory passages ; this is not remarkable, when we 

 consider the greater complexity of the organs of digestion and 

 the varied conditions which they present with regard to microbial 

 invasion. 



The buccal cavity, so exposed to the entry of extraneous micro- 

 organisms along with the food and the external air, has a very rich 

 microbial flora, in which Miller 2 , the author of our most complete 

 work on this subject, has recognised in man more than thirty species. 

 Several representatives of this flora, e.g. the Leptothrix and the 

 Spirochaeta are constantly present, and are very characteristic of 

 the buccal cavity of man. With them are frequently found pneumo- 

 [435] cocci, staphylococci, and streptococci, whose pathogenic power is 

 undoubted. Virulent diphtheria bacilli are also met with in a certain 

 number of quite healthy persons. It is astonishing that, in spite of 

 this state of things, wounds in the mouth heal very rapidly, and 

 operations on the buccal cavity done with insufficient or no aseptic 

 precaution do not, in the great majority of cases, set up infective 

 complications of the slightest importance. After certain buccal 

 operations we are often confronted with a complicated and open 

 fissure ; nevertheless the wound thus left exposed is not ordinarily 

 the seat of any infection either local or generalised. 



1 Compt. rend. Soc. de biol., Paris, 1897, p. 265. 



2 " Die Mikroorganismen der Mundhohle," Leipzig, 2 te Aufl., 1892. 



