180 HOW PLANTS BENEFIT AND HARM MANKIND 



of the mouth or nose, from air, food, or water, or may be trans- 

 mitted from some person having disease to a well person by con- 

 tact. Usually the germs enter the body through some opening, 

 as the mouth, or through a cut or sore. With care by the civic 

 authorities and by individuals a healthy person should easily keep 

 from such diseases, if he takes proper precautions. 



Tuberculosis. The one disease responsible for the greatest 

 number of deaths perhaps one seventh of the total on the globe 



is tuberculosis. But this dis- 

 ease is slowly but surely being 

 overcome. It is believed that 

 within perhaps fifty }^ears, with 

 the aid of good laws and sani- 

 tary living, it will be almost 

 extinct. 



Tuberculosis is caused by 

 ^ ie row th of a bacterium, 

 called the tubercle bacillus, 

 within the lungs or other tis- 

 sues of the human body. Here 

 it forms little tubers full of 

 germs, which close up the deli- 

 cate air passages in the lungs, 



V 



/ 



* 





Microscopic appearance of ordinary milk 

 showing fat globules and bacteria. The 

 cluster of bacteria on left side are lactic- 

 acid-forming germs. Tuberculosis germs 

 are sometimes found in milk. 



and in other tissues give rise to 

 hip-joint disease, scrofula, lupus, 

 and other diseases, depending 

 on the part of the body they attack. Tuberculosis may be con- 

 tracted by taking the bacteria into the throat or lungs by eating 

 meat or drinking milk from tubercular cattle. Especially is it com- 

 municated from a consumptive to a well person by kissing, drink- 

 ing, or eating from the same cup or plate, using the same towels, 

 or in any way coming in direct contact with the person having the 

 germs in his body. Although there are always some of the germs in 

 the air of an ordinary city street, and though we may take some 

 of these germs into our bodies at anytime, yet the bacteria seem able 

 to gain a foothold only under certain conditions. It is only when 

 the tissues are in a worn-out condition, when we are " run down," 

 as we say, that the parasite may obtain a foothold in the lungs. 



