STUDIES OF SPORE-PLANTS 291 



259. Diseases Caused by Bacteria. We are so familiar 

 with the idea that many diseases are caused by " germs " or 

 bacteria, that it seems scarcely possible that less than thirty 

 years ago no disease had been shown to result from the 

 growth of bacteria in the human body. It was in 1876 

 that Robert Koch, of Berlin, made pure cultures of rod- 

 shaped bacteria found in the blood of cattle and sheep 

 suffering from anthrax, or splenic fever, and gave the first 

 proof that bacteria caused disease. Six years later (1882) 

 Dr. Koch demonstrated beyond question that human tuber- 

 culosis is caused by a bacterium which he named Bacillus 

 tuberculosis ; and in 1883 he proved that the dreaded dis- 

 ease, Asiatic cholera, is caused by another specific bacterium. 

 These discoveries aroused the interest of many investigators, 

 with the result that in less than thirty years there has been 

 built up the new science of bacteriology, which has already 

 been of inestimable benefit to the human race and bids 

 fair to lead soon to absolute control of some of the most 

 dangerous diseases. 



To-day the list of diseases known to be caused by bacteria 

 is a long one and each year becomes longer. The following 

 are some of the best known: tuberculosis of any organ, 

 cholera, diphtheria, typhoid fever, blood-poisoning, syphilis, 

 pneumonia, meningitis, gonorrhea, influenza, tetanus, lep- 

 rosy, bubonic plague, and numerous others of rarer occur- 

 rence. These are all infectious, or germ diseases; and some 

 of them are also contagious, or liable to be transmitted by 

 contact with patients. 



260. Diseases Caused by other Micro-organisms. A 

 number of diseases are now known to be caused by micro- 

 organisms which are animals, while the bacteria belong to 

 the plants. These animal parasites are one-celled, and 

 belong to the group of the Protozoa ( 273). The terrible 

 African disease known as sleeping sickness, malaria, and a 

 form of dysentery are the best known human diseases cer- 



