56 PRINCIPLES OF SOIL MICROBIOLOGY 



drawing up individual cells by means of the Barber capillary pipette 

 and transferring them to specific sterile liquid media. The micro- 

 manipulator of Chambers 7 may also be employed. 



In view of the fact that the bacteria live and act in the soil in mixed 

 culture, important information is obtained not only from the study of 

 pure cultures, but also from mixed cultures, either crude or artificially 

 prepared. 



For a description of pure cultures of bacteria, the Chart of the Society 

 of American Bacteriologists can be used . 8 • 9 This includes a study of the 

 important morphological, physiological and cultural characteristics 

 of the organisms. However, the chart can not be readily utilized in 

 the description of most of the soil bacteria with the exception of some 

 of the heterotrophic bacteria requiring combined nitrogen, especially 

 the spore-forming organisms. 10 



Differentiating characters of bacteria. The size of the organisms is a 

 variable factor with rather large limits of variation which depend upon 

 the nutrient media in which the cells are grown and various environ- 

 mental conditions. 11 However, in the case of the spore-forming bacteria, 

 the size of the spore is of great diagnostic value. Motility of bacteria 

 has been utilized in the classification of Migula but the constancy and 

 value of this character have been questioned by Lehmann and Neu- 

 mann, 12 who found the presence or absence of spore production by 



7 Chambers, R. New micromanipulator and methods for the isolation of a 

 single bacterium and the manipulation of living cells. Jour. Inf. Dis. 31 : 334-343, 

 344-348. 1922. 



8 Harding, H. A. The constancy of certain physiological characteristics in the 

 classification of bacteria. N. Y. Agr. Exp. Sta. Tech. Bui. 13. 1910. 



9 Rahn, O., and Harding, H. A. Die Bemi'ihungen zur einheitlichen Beschrie- 

 bung der Bakterien in America. Centrbl. Bakt. II, 42 : 385-393. 1914. 



10 The methods used in the description of these organisms are discussed in the 

 various Reports of the Committee on Bacteriological Technic of the Society of 

 American Bacteriologists. C. B. T. Methods of pure culture study. Jour. 

 Bact. 3: 115-138. 1918; 4: 107-132. 1919; 5: 127-143. 1920; 7: 107-132. 1919. 

 Conn, H. J. et al. Recent work on the descriptive chart and the manual of 

 methods. Ibid. 10: 315-319. 1925. Also Conn, H. J. Soil flora studies. II. 

 Methods best adapted to the study of the soil bacteria. N. Y. Agr. Exp. Sta. 

 Tech. Bui. 57: 18-42. 1917. 



11 Lohnis, F., and Smith, N. R. Life cycles of bacteria. Jour. Agr. Res. 

 6: 676-702. 1916; 23: 401-432. 1923; also Lohnis, 1921 (p. 55); Scales, F. M. 

 Induced morphologic variation in B. coli. Jour. Inf. Dis. 29: 591-610. 1921. 



12 Lehmann, K. B., and Neumann, R. O. Atlas und Grundrisz der Bakterio- 

 logie. Mi'inchen, Lehmann's. 1920. 



