PREFACE TO THE FIRST EDITION 



On the basis of their relation to man, the microscopic forms of life may 

 be classified in two major groups: pathogenic forms that attack living 

 systems, especially those useful to man and to his domesticated plants 

 and animals } and saprophytic forms that attack inanimate matter, in- 

 cluding the universal scavengers and the organisms utilized in industry 

 and in the preparation of foodstuffs. Between true parasitism — one or- 

 ganism living in or upon the body of another — and true saprophytism 

 — one organism merely destroying the waste products and the dead 

 cells of another — are groups of relationships that may be designated as 

 antagonistic and associative. In the first of these, one organism is in- 

 jured or even destroyed by the other, whereas in the second, one or- 

 ganism assists the other and may in turn be benefited by it. 



The antagonistic interrelationships among microorganisms have at- 

 tracted attention since the early days of bacteriology. Following the 

 discovery by Pasteur that microbes are responsible for certain human, 

 animal, and plant diseases, it was established that other organisms, later 

 designated as antagonists, are able to combat and even destroy the dis- 

 ease-producing agents. At first the soil was believed to be the natural 

 habitat of the bacteria that cause epidemics and disease as a whole, but 

 after careful study the fact was definitely established that very few of 

 these bacteria survive for long in the soil. On the contrary, the soil was 

 found to be the natural medium for the development of antagonists 

 chiefly responsible for the destruction of pathogens. The saprophytic 

 organisms that influence in various ways the disease-producing bacteria 

 and fungi were found to inhabit, in addition to the soil, various other 

 natural substrates, such as manure heaps and water basins. 



The activities and potentialities of these antagonistic microbes still 

 present many problems. Little is known about the nature and mode of 

 formation of the antibiotic substances they produce, and even less about 

 the mode of their action. The substances vary greatly in their physical 

 and chemical properties. Some are soluble in water, others in ether, alco- 

 hol, or other solvents. Some are thermolabile, others are thermostable. 

 Some are sensitive to alkalies or to acids, others are not. Some are 



