164 BACTERIA OF DISEASE 



condition there is only slight danger of the organism gaining a 

 foothold. Just how the system is able to combat the growth of 

 these plants is now the subject of earnest investigation. Certain 

 diseases, as mumps, measles, whooping-cough, smallpox, etc., 

 usually occur but once and it is probable that substances are 

 formed in the body as a result of the presence of the bacteria or 

 animal organisms that prevent a second growth of the germs and 

 the individual thus becomes immune to further attacks. The 

 formation of such a substance is known to occur in the case of 

 diphtheria. The bacteria of this disease occur in the upper air 

 passages of the throat and secrete a poison or toxine that affects 

 the entire body. Gradually the system forms a substance called 

 an antitoxine that stops the growth and eventually kills the bac- 

 teria. The vigor of the system and the virulence of the bacteria 

 decide whether the disease shall prove fatal before the anti- 

 toxines are formed in sufficient quantity to destroy the bacteria. 

 Note that these disease-producing bacteria vary in their power 

 to produce toxine. Sometimes, as in epidemics, they are so 

 virulent as to attack with fatal results the strongest individuals. 

 In other cases the bacteria appear to be degenerate and only pro- 

 duce mild symptoms of the disease. This is the principle of 

 vaccination. The little animals causing smallpox are cultivated 

 under conditions that weaken them and render them less virile. 

 Consequently when they are introduced into the system they pro- 

 duce only mild symptoms of the disease. The history of the 

 study of bacteria constitutes one of the most interesting and 

 fascinating pages in science. Pasteur was the first to demon- 

 strate that fermentations and putrefactions, and later that 

 certain contagious diseases, were due to bacteria and animal 

 organisms. His work is now commemorated by a tablet on the 

 rue Pasteur in Paris with the inscription: Here stood Pasteur's 

 laboratory. 1857 Fermentations; 1860 Spontaneous Genera- 

 tion; 1865 Diseases of Wines and Beers; 1881 Virus and Vaccini; 

 1888 Silk-worm Distempers; 1864-1888 Hydrophobic Remedies. 

 To-day every state and government has its corps of workers and 

 every city its expert bacteriologists who are studying the nature 

 of bacteria and their relation to plants and animals. 



