Recent DcNclopmciits and Perspectives 25 



specificity of legume bueteria; of Viitanen, P. S. Wilson, F. E. Allison, 

 and others on the chemistry of the nitrogen-fixation process; of 

 Lohnis on the life cycle of Azotobactcr; and of Christenseii, Gainey, 

 and others on the influence of environmental conditions, such as 

 reaction, upon the growth and activities of these bacteria in the soil. 



This period was also marked by new methods for the study of 

 soil microorganisms, notably the soil-staining, contact slide, and 

 direct soil examination, introduced, respectively, by H. J. Conn and 

 Winogradsky, by Rossi and Cholodny, and by Kubiena. These meth- 

 ods yielded additional information on the soil microscopic population. 



The appearance in 1927 and in 1932 of Principles of Soil Micro- 

 biology by \\^iksman closes this chapter in the history of the subject, 

 just as Lohnis' and Lipman's books closed the previous chapter. 



Recent Developments and Perspectives (1940-1950) 



World War II disorganized the normal course of development of 

 many sciences, including that of soil microbiology. When the plow- 

 share was set aside for the sword, peaceful pursuits had to give way 

 to those which would help in winning the war and in alleviating 

 human suffering. The soil microbiologist did not set aside his micro- 

 scopes and his test tubes, his Petri dishes and his retorts; he used 

 them for other purposes. Chief among these were studies resulting 

 directly or indirectly from the war eftbrt. The search centered on 

 finding (a) methods for combating fungi causing spoilage of sup- 

 plies and essential materials, (b) means of meeting possible attacks 

 from the enemy, who might be tempted to utilize poisonous gases 

 and bacterial warfare or to use microorganisms for killing cultivated 

 plants, and finally (c) microorganisms capable of producing chem- 

 ical substances which could be used as chemotherapeutic agents for 

 combating infections and epidemics. 



In the development of antibiotics, the soil microbiological popula- 

 tion has contributed more than its share. It is to the soil that the 

 microbiologists came in search of new antibacterial agents. In the 

 isolation of the numerous antibiotics, organisms were utilized that 

 came either directly from the soil or indirectly through the dust of 

 the atmosphere. Thus came gramicidin and tyrocidine, as well as 

 the many other bacterial products; penicillin, gliotoxin, claxacin, and 

 other fungus products; actinomycin, streptothricin, streptomycin, 

 chloramphenicol, aureomycin, terramycin, and neomycin, produced 

 by actinomycetes. This field is still far from exhausted; and, although 



