These germs get blown about in the air with the dust, and get into other people's mouths, and so into their lungs—that is, if the other people go about with their mouths partly open. If they breathe through their nose only, as I hope all Scouts do, there is less chance of the germs getting into the lungs, as they get caught in the sticky liquid in the nostrils, and get driven out again when you blow your nose.
It is the same with other diseases besides consumption.
The Missioner Scout can safely go about among people who are ill with colds, measles, and other sicknesses, if he breathes only through his nose. All illnesses that are "catching" are spread by germs flying from one person to another.
The consumptive germs get into you and go for your lungs, which are big sponges inside you, through which your blood gets the air, which is necessary to keep it healthy. Consumption germs "consume" your lungs.
The nasty little germ of disease thrives in dirt, and dark and muggy air, and so he grips even the healthiest people in rooms that are dark and dirty, and where the windows are not kept open.
Fresh air, sunlight, and cleanliness kill the germs.
Now that you know what consumption is, you will be doing a good turn to get other people to understand it.
I want every Scout who reads this to show the pictures to at least five other people, AND EXPLAIN them. He may thus save lives.