122 Physiology. 



a kind of living germ or spore that has gotten into it from 

 the dust on the fruit before it was crushed, or from dust 

 in the room. Boil the cider to kill the spores already in 

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

 will not ferment. These are a few instances of kinds of 

 living dust that do not affect human beings any more 

 than so much dead matter. 



Disease Germs. 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 

 of some of these spores in our bodies. Our bodies are a 

 good soil for certain germs. The germs that cause con- 

 sumption, typhoid fever, Asiatic cholera, erysipelas, diph- 

 theria, lockjaw, and the grippe, 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, measles, mumps, whooping-cough, and 

 scarlatina are caused by germs, but these diseases have 

 not been studied so successfully. 



How to avoid Germs. 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 think 

 about, is too terribly true to allow of being called an imag- 

 ined case. 



The Danger from Consumption. A consumptive spits 

 on the pavement. In this sputum are probably hundreds, 

 if not thousands, of germs known as bacilli (Bacillus tuber- 



