412 ON THE ORIGIN, PROPAGATION, 



of infected dust upwards. Its hygroscopic qualities in 

 great part prevent this. When dried sputum is re- 

 duced to powder in a humid place, it attracts to itself 

 moisture, and collects into little balls. The streets in 

 which phthisical persons expectorate are rendered in- 

 nocuous by rain, or by the artificial watering common 

 in towns. Cornet regards this watering as an enormous 

 sanitary advantage. No doubt when dry east winds 

 prevail for a sufficient time, infectious dust will mingle 

 with the air. During easterly winds infectious diseases 

 are known to be particularly prevalent. Our sufferings 

 from influenza during the present year have been con- 

 nected in my mind with the long-continued easterly 

 and north-easterly winds, which, sweeping over vast 

 areas of dry land, brought with them the contagium that 

 produced the malady. Besides the difficulty encountered 

 before the sputum reaches the state of very fine powder, 

 other difficulties are presented by the numberless angles 

 and obstacles of the respiratory tract, and by the 

 integrity of the ciliary-epithelium, to the more or less 

 vigorous action of which is due the fact that amid 

 thousands of opportunities we have only here and there 

 a case of infection. 



The action of the tubercle bacillus is determined by 

 the state of the surface with which it comes into con- 

 tact. Wounds or lesions, caused by previous diseases, 

 such as measles, whooping cough, and scarlatina, may 

 exist along the respiratory canal. By illness, moreover, 

 the epithelium may be impaired, the inhaled bacilli 

 being thus offered a convenient domicile. If it be 

 thought desirable to call such a state of things ' pre- 

 disposition,' Cornet will raise no objection. Wherever 

 a wounded or decaying tissue exists the bacillus will 

 find, unopposed, sufficient nutriment to enable it to in- 

 crease in number, and to augment in vigour, before it 



