702 THE AMERICAN NATURALIS7\ [VOL. XXXIX. 



region of protoplasm as in the Cyanophyceae. There is of course 

 no blue-green pigment (phycocyan) in the cells of bacteria and 

 consequently no chromatophore but several sorts of inclusions 

 may be present in the protoplasm. The nature of some of the 

 inclusions is not clear and this subject has not been given as 

 much attention as in the Cyanophyceae. It is significant that 

 this cell structure should be found so clearly in the Beggiatoa 

 since this organism seems very close to Oscillatoria in its mor- 

 phology. Some of the larger species of Beggiatoa may be 

 expected to yield conclusions similar to those of Olive's investi- 

 gation on Oscillatoria if sectioned and critically stained, especi- 

 ally as 1 the cells are very large in some forms and there is 

 probably less extraneous matter to complicate the interpretation 

 of the preparations. 



As has been stated, investigations upon the smaller species of 

 bacteria and especially upon pathogenic forms have met with 

 great difficulties. These led at one time to the ingenious theory 

 of Biitschli ('90), followed by Zettnow ('97) that possibly the 

 entire protoplast had the value of a nucleus. That is to say, 

 an outer peripheral region of cytoplasm had either never been 

 developed in these organisms or, if present, had become so 

 closely associated with the chromatin that it could not be dis- 

 tinguished as a special region of the cell. A peripheral region 

 of cytoplasm is represented in some of the larger forms by the 

 cilia and by accumulations of protoplasm at the ends of the cells, 

 especially clearly shown in Spirillum (Biitschli, '96 ; Zettnow, 

 '97). Later Zettnow ('99) and Feinberg (: oo) applying the 

 staining method of Romanowski, followed by several later inves- 

 tigators with improved technique (Nakanishi, :oi,and others), 

 succeeded in differentiating a minute body in the cells of smaller 

 bacteria and pathogenic forms, which is regarded now as similar 

 to the central body of the sulphur bacteria and a true nucleus. 

 This structure is very minute since it occupies a portion of 

 these exceedingly small cells. Naturally it will be very difficult 

 to obtain any detailed knowledge of its structure and behavior 

 during cell division. But enough seems to be known to justify 

 the belief that differentiated nuclear structures are probably 

 present even in the smallest types of bacteria. A recent paper 



