BACTERIA I 97 



of the grains which compose this filament (Fig. 75, 12 and 13). An 

 interesting variation of this structure is found ii^ B. saccobrinchi. 

 In this bacillus is noticed first an initial stage where the nucleus is 

 represented by an axial filament quite similar to that oiB.spirogyra 

 (Fig. 75, 14). In the course of development, however, this filament 

 resolves itself into a great many grains which scatter through the 

 cell (Fig. 75, IS and 16). The nucleus then becomes diffuse. Part of 

 this diffuse nucleus next condenses at the time of sporulation into a 

 large chromatic grain which forms the beginning of the spore. Finally, 

 in other baciUi, Dobell finds in the whole development no more than a 

 diffuse nucleus, that is, the structure described by Schaudinn and by 

 Guilliermond. 



In the group of spirilla, Dobell notices these three types of structure: 

 In some species he finds present a spherical body resembUng a nucleus; 

 other species show a zigzag or a spiral filament; still others have a 

 diffuse nucleus. 



From these observations, Dobell feels authorized to conclude that 

 bacteria are organisms originally containing a nucleus, but in which the 

 nucleus, as a result of parasitism, has undergone a series of retrogres- 

 sions which have ended by making it diffuse. 



This opinion would have the advantage of reconciUng opposed 

 theories. It would explain how some authors have been able to dis- 

 cern a true nucleus in various forms. 



Another more weighty reasoning which might also explain these 

 contradictions is the fact that under the name of bacteria are gathered 

 forms perhaps very different, some of which seem to belong to the 

 Stdfo-bacteria and others might be considered as molds. 



Although we have just mentioned numerous works, the conclusion, 

 to my mind, would be that while some bacteria may contain a more or 

 less rudimentary nucleus whose e3?istence is nowhere else precisely 

 demonstrated, so far, in the great majority of the species, nothing more 

 has been found than a diffuse nucleus consisting only of grains of chro- 

 matin scattered through the cytoplasm. 



Lite Cycle of Bacteria. — The Editor feels justified in adding 

 to the foregoing review the very recent work of Lohnis and Smith, 

 Journal of Agricultural Research, Vol. VI, No. 18, July 31, 1916, 

 because, both for its suggestiveness and presentation of experimental 



