It is a well-known fact that a large percentage of deaths among factory operatives is due to consumption. While perhaps some of this may be traced to the environment of the home, many cases are contracted in the factory from people who are in the early stages of the disease. The reason lies in the fact that in every act of spitting, coughing, sneezing, and speaking, minute droplets of saliva, which may contain tuberculosis germs (specific bacilli), are sent forth into the air, in which they remain suspended for some time. The spitting consumptive is usually a victim of the disease long before it is known. Sputum cast about upon the floor and elsewhere becomes dried on exposure to the air and then ground to powder, the bacilli spreading in all directions.

Enough has been said to show the need of a systematic method of removing the waste gases, dust, etc., from rooms and buildings. Natural agencies, like the air, that pass through the cracks of floors, doors, and windows may be sufficient to remove some of the carbon dioxide of a dwelling house by replacing it with new air, but in a factory where hundreds of people are employed in the same rooms this method is ineffective.