18 BACTERIOLOGY AND PROTOZOOLOGY 



HISTORY. 



The existence of more or less independent forms of life 

 invisible to the naked eye was first proven about two and 

 one-half centuries ago by Van Leeuwenhoek and Kircher, 

 who actually saw and described what were called animalcule, 

 living, moving, and multiplying bodies in the tartar from 

 teeth and in animal fecal matter. The first conception of 

 the existence of such microscopic forms cannot be accredited 

 to these observers, since so long ago as in the fourth century 

 B.C. Aristotle suggested the possibility. 



As might be expected, these single-celled bodies were 

 not seen until the development of lens-making permitted 

 accurate enlargement. The greatest advances have been 

 made, furthermore, since the perfection of the compound 

 microscope in the early years of the nineteenth century. It 

 is also noteworthy that those who might be considered the 

 founders of this science, so important to physicians, were 

 botanists and chemists. The most important consideration 

 for the early observers was the relation that these minute 

 bodies bore to the spoiling of food and water, most physicians 

 of the past having discredited the relation of bacteria to 

 disease. The scientific world now grants that communicable 

 diseases are due to some forms of living virus. The first 

 opinion upon the relation of specific disease-producing 

 bacteria came in the middle of the eighteenth century, bu*; 

 such a theory could not be proven until about thirty years 

 ago, when Koch made it possible to separate the various 

 individual bacterial species and enabled us, by a series of 

 postulates, to study the relation of the germs to their par- 

 ticular disease. The great proof of the existence of bacteria 

 came from the man who may be considered the founder of 

 the modern science of bacteriology, Louis Pasteur, a French 

 chemist, who demonstrated beyond question that bacteria 

 produce fermentation, and that fermentable materials, if 

 protected from the air, remain without bacteria. There 



