CYTOLOGICAL STUDIES OF A20T0BACTER 

 CHROOCOCCUM ' 



By AUGUSTO BONAZZI, 



Assistant in Soil Biology, Department of Soils, Ohio Agricultural Experiment Station 



INTRODUCTION 



Because of its advantage to agriculture, the maintenance of a nitrogen 

 balance in the soil has long been studied by scientists. Among the lower 

 organisms involved in this phase of agricultural economy the Azotobacter 

 group, first described by Beijerinck (2)^ in 1901, is surely one of those 

 that deserve very close study because of their extreme importance. 



Since the first work of Berthelot (4) on nitrogen fixation by soil, the 

 Clostridium and Azotobacter groups have been discovered and the meth- 

 ods for their study have been brought to the standard basis, so that 

 these organisms can now be justly compared to any other organism 

 belonging to the class of the Protista. Unfortunately, not till very 

 recently has the cytology of Azotobacter chroococcum been studied. But 

 since cytology in all the applications of bacteriology, such as patho- 

 logical bacteriology and the bacteriology of the tanning, retting, and 

 fermentation industries, has been overlooked by many, it is not surpris- 

 ing that such studies have been deemed unnecessary or unimportant in 

 agriculture. 



It is a rational hypothesis very often expressed that every change in 

 physiological activities is accompanied by a like change in the cytological 

 structure of an organism. 



Unfortunately, with our present methods, there is no possibility of 

 studying changes in structure, especially if these are small, with that 

 accuracy which it is possible for us to employ in detecting changes in 

 physiological activities. 



Furthermore, the majority of methods commonly used in bacterio- 

 logical studies, especially the staining methods and processes, are only of 

 a diagnostic and medical value, unsuited for refined work. More delicate 

 methods should be used if very slight differences in structure are to be 

 detected. 



Although the size of A. chroococcum makes the organism ideal 

 for a cytological study, it has been completely ignored for years. Its 

 biological functions play such a great role in the nitrogen cycle in nature 



1 Thanks are due to Dr. E. R. Allen, under whose direction this work was undertaken, for kind advice 

 and criticism. 

 * Reference is made by number to "Literature cited," p. 238-239. 



Journal of Agricultural Research, Vol. IV, No. 3 



Dept. of Agriculture, Washington, D. C. June 15, 1915 



Ohio— I 



91007°— 15 3 (225) 



