HISTORY OF SOIL MICROBIOLOGY 835 



Beginnings of soil microbiology. Each science has its roots and ante- 

 cedents in the past and each is developed out of the materials of the 

 past. This is true particularly of soil microbiology, which has de- 

 veloped directly from the empirical practices in agriculture and as a 

 result of the advances made by the science of bacteriology; it owes a 

 great deal to the older sciences, botany and its daughter science my- 

 cology, zoology and its offspring protozoology, chemistry, physics, 

 and especially these sciences as applied to soil processes. 



Among the empirical practices, we need mention (1) the beneficial 

 influence of the growth of legumes upon subsequent crops, (2) the 

 composting of manure or various farm wastes, (3) the burning of the 

 upper layer of soil to insure better crops, (4) the addition of fertile soil to 

 soil newly prepared from bogs. The progress of physics resulted in the 

 development of the microscope and balances. The progress of chemis- 

 try resulted in a knowledge of the chemical composition of matter, a 

 better understanding of the composition of complex proteins and car- 

 bohydrates, and in the development of various methods used in or- 

 ganic and inorganic analysis. The development of physical chemistry 

 resulted in the progress of our understanding of the nature of colloids 

 and surface phenomena, of the hydrogen-ion concentration of the 

 medium, oxidation and reduction processes. All have contributed to 

 the development of soil microbiology. The study of the microorganisms 

 themselves dates back to the work of Kircher and Leeuvenhoek (1683), 

 who made the first observations on the bacteria, followed by the investi- 

 gations of 0. G. Miiller (Animalcula infusoria, 1786), Ehrenberg 1 and T. 

 Schwann. 2 The last demonstrated that yeast was a living organism. The 

 science of botany has contributed to a better knowledge of the mor- 

 phology and physiology of fungi and algae. The science of zoology ad- 

 vanced our understanding of the protozoa, nematodes and other inverte- 

 brates found in the soil, especially in respect to their nutrition and relation 

 to the other members of the soil population. Bacteriology, beginning 

 with the work of Pasteur on microorganisms as chemical agents, has 

 been one of the most fruitful fields in stimulating the development of 

 soil microbiology. Both the medical and agricultural bacteriologists 

 have made important contributions. It is sufficient to mention the 

 methods of pure culture study of bacteria, finally leading to a differen- 

 tiation of microorganisms on a physiological basis; the plate method 

 for counting and isolating bacteria; the introduction of selective enrich- 



1 Ehrenberg. Die Infusionstierchen als vollkommene Organismen. 1839. 

 1 Schwann, T. Gilbert's Ann. Phys. u. Chemie., 51: 1837. 



