528 ZOOLOGY 



Some of the steps in the progress of medicine have been 

 outlined heretofore. Many of the early biologists we have seen 

 to be physicians. 



Leeuwenhoek, one of the early users of the microscope, dis- 

 covered bacteria in 1687. Soon after this it- was first suggested 

 that microscopic forms might have something to do with con- 

 tagious diseases. In 1840, Heale took the position that all such 

 diseases are caused by germs. 



Louis Pasteur (1822-1895), a Frenchman, was one of the 

 most remarkable scientists of all time. He discovered that 

 fermentation is due to microscopic organisms (1857) ; established 

 the actual connection between certain germs and the diseases 

 produced by them; showed that germs could be made less 

 harmful by being grown in certain conditions, and that these 

 attenuated germs would produce only a mild form of the 

 disease which would, however, give immunity just as fully as 

 the severer forms. He succeeded in inoculating against fowl 

 cholera, splenic fever of cattle, and finally a;gainst hydro- 

 phobia. In the institute which bears his name similar principles 

 have been extended to bubonic plague, lockjaw, and other 

 diseases. Here also was discovered the antitoxin for diphtheria. 

 Robert Koch, born in 1843, is the Pasteur of Germany. He 

 discovered and isolated the germ of tuberculosis (1881) and of 

 Asiatic cholera (1883). Sir Joseph Lister the great English 

 surgeon, bom in 1827, using Pasteur's discoveries first applied 

 antiseptics to wounds in order to destroy the germs that might 

 enter. This was the foundation of aseptic surgery which under- 

 takes so to sterilize everything brought near an operation that 

 germs shall not enter at all. 



One of the most interesting things to hold in mind about 

 biological discoveries is this : it is impossible to tell how impor- 

 tant to human welfare any discovery may prove to be. No one 

 could have imagined that these students with the microscope 

 studying the organisms of decomposition would be led gradually 

 to the most profoundly important facts bearing on human life. 

 It was not quite 200 years from the discovery of bacteria until 

 Pasteur had discovered a way to overcome some of the diseases 

 produced by them. Similar biological work done upon other 



