DISEASE GERMS. 145 



as we call them, that will grow in suitable places and condi- 

 tions. So, too, from a patch of mold, when brushed, we 

 often see a little cloud of dust. These are a few instances 

 of kinds of living dust that simply act on us like so much 

 dead matter. 



If we set a tumbler of cider on a table in a warm room, in 

 a few days it ferments. This is due to yeast that has gotten 

 into it. Boil the cider to kill any yeast that is already in it, 

 and cork it securely so that air cannot get at it, and it will 

 not ferment. Dried yeast germs float in the air, settle into 

 this exposed cider, and cause it to ferment. Cider is a good 

 soil for yeast. But there are floating in the air many kinds of 

 spores that may grow in our bodies. We know that many of 

 our contagious diseases are due to the growth in our bodies 

 of some, of these spores. Our bodies are a good soil for cer- 

 tain germs. The germs that cause consumption, typhoid-fever, 

 Asiatic cholera, erysipelas, diphtheria, and some forms of blood- 

 poisoning, are well known. Microscopists know them when 

 they see them as readily as we know peas from beans. And 

 it is proved beyond all doubt that these germs get into our 

 bodies by being breathed in, or by being eaten in food, or in 

 drinking water, or by introduction into the blood in wounds. 

 We have reason to believe that small-pox, yellow-fever, mea- 

 sles, and scarlatina are caused by germs; but these diseases 

 have not been studied so successfully. 



How can we avoid or get rid of dusts of these kinds ? 



To exterminate any plant, we try to keep the seeds from 

 ripening, and to kill all that do ripen. Let us take a case 

 that, while not pleasant to contemplate, is too terribly true to 

 allow of being called an imagined case. 



A consumptive expectorates on the pavement. In this 

 sputum are probably hundreds, if not thousands, of germs 

 known as bacilli (Bacillus tuberculosis). They are alive. 



