PROBLEM 2. Hoiv TIV Cav Cojupier Some Diseases 



323 



Fig. 293 /f chest x-rays were taken of all peo- 

 ple periodically, hmg tuberculosis would be 

 detected and cojdd be reduced, (boston tuber- 

 culosis association) 



wine, wine to vinegar, and caused milk to 

 sour. These are all chemical changes. In 

 the making of beers and wines yeast plants 

 partially oxidize sugar, producing alco- 

 hol and carbon dioxide. This incomplete 

 oxidation is called fermentation. Bacte- 

 ria also carry on fermentation or incom- 

 plete oxidation when they sour milk by 

 producing lactic acid and when thev 

 spoil or sour wines by changing alcohol 

 into acetic acid. 



This work of Pasteur was of great 

 practical importance to the wine indus- 

 try because methods were soon found to 

 prevent the growth of bacteria that 

 caused the spoiling of wines. It was of 

 even greater importance in quite a dif- 

 ferent way. Our understanding of fer- 

 mentation paved the way for the germ 

 theory of disease. Pasteur was soon con- 

 vinced that disease bacteria could bring 

 about changes in the body in the same 

 way that they could change liquids in a 

 flask. 



Pasteur turns to the study of disease. 

 Convinced of the truth of the germ 



Fig. 294 A Board of Health worker examining 

 Petri dishes. Which step might this be iji de- 

 ciding that a disease is caused by a specific 

 germ? (new york uty board of health) 



theory of disease, Pasteur devoted his 

 attention to the study of immunity of 

 animals to disease. With the help of his 

 assistants he raised pathogenic bacteria 

 of many kinds in his laboratory. Among 

 others, he raised pure cultures of the bac- 

 teria which caused cholera (coll'er-a) in 

 chickens. One day he discovered, largely 

 by accident, that when he kept these cul- 

 tures for some time the bacteria seemed 

 to become weaker. He came to this con- 

 clusion because he noticed that when 

 such cultures were injected into healthy 

 birds they did not die, although they be- 

 came ill. When he inoculated (in-oc'you- 

 lated) these same birds, after their re- 

 covery, with a fresh culture of cholera 

 germs, they did not contract the disease. 

 Why not cultivate such weakened germs 

 in large numbers and make a practice of 

 inoculating healthy birds with them? If 

 an epidemic of chicken cholera should 

 occur these birds could then, perhaps, 

 resist the disease. Pasteur tried this and it 

 worked. When the next cholera epi- 

 demic came, none of the inoculated birds 



