70 DUST AND ITS DANGERS. 



exhaled air of consumptives, no matter how 

 seriously ill, is not dangerous ; it carries no 

 germs. It is only the solid discharged mate- 

 rial of the sputum which carries the danger. 

 And this sputum, moist and usually adherent 

 as it is when fresh, is only dangerous, so far as 

 contamination of the air is concerned, when it 

 is permitted to dry. 



Here we seem to be at the root of the evil. 

 The reason why consumption is so widespread 

 and the most important element in this appall- 

 ing mortality is simply that consumptive per- 

 sons, either from ignorance or carelessness, are 

 distributing the poison not only everywhere 

 they go, but everywhere the dust goes which 

 has been formed in part by the undestroyed 

 germ-laden material expelled from their lungs. 

 This is what has been mistaken for so many 

 years as evidence of the hereditary transmis- 

 sion of consumption, as proof that consumption 

 " runs in families." The house-mates have 

 unwittingly poisoned one another, usually, no 

 doubt, through the dust. We are but just be- 

 ginning to recognize this. We have, indeed, 

 known what caused consumption but a very 



