July 3i, 1916 Life Cycles of the Bacteria 677 



pletely overlooked. In fact, this slime or granulated dirt has been 

 merely an annoying occurrence on the slides of thousands of bacteriolo- 

 gists. Acetic acid and many other remedies have been recommended to 

 insure clean preparates. Of course, beef broth and some other sub- 

 strates usually give really dirty smears which need some cleaning, but 

 we have been much too radical in this direction. Under certain condi- 

 tions all bacteria pass over into a "symplastic" stage, appearing under 

 the microscope as either an unstainable or a readily stainable mass with- 

 out any visible organization, which, if not discarded as dead, later gives 

 birth to new regenerated forms frequently of very characteristic and 

 unusual appearance. 



As practically all our new knowledge of the life cycles of the bacteria 

 has been derived from a renewed study of B. azotobacter, the behavior of 

 this organism will be described first. 



Before we enter into this subject, however, we beg to point out that by 

 discussing the life cycles of the bacteria we do not intend to revive any 

 of those unclear theories concerning bacterial polymorphism or pleomor- 

 phism. The development of the bacteria is characterized not by the 

 irregular occurrence of more or less abnormal forms but by the regular 

 occurrence of many different forms and stages of growth connected with 

 each other by constant relations. 



Unquestionably many so-called species frequently described in the 

 most superficial manner will have to be canceled, because they merely 

 represent fragments of the life cycles of other bacteria. "Good" species, 

 on the other hand, will not only keep their position, but they will receive 

 a much more complete and sharper definition than they now have. 

 Moreover, the discovery of the symplastic stage opens the way to answer 

 by exact experiments the question concerning species or varieties. 



THE LIFE CYCLE OF BACILLUS AZOTOBACTER 



In text figure 1 is given a schematic sketch of the development of 

 B. azotobacter according to our present knowledge. The letters A to M 

 indicate the different types of growths which are separated from each 

 other by broken lines. The single- and double-pointed arrows show the 

 connections between the different forms as they have actually been 

 observed. Each of the four circles contain in each case all those forms 

 which have heretofore been considered by cai'eful investigators as repre- 

 senting sufficient basis for establishing a species. Observers of the more 

 usual, less painstaking class, however, have been onty too much inclined 

 to form new species even inside these subcycles. For example, the dif- 

 ferent types of spore-free and spore-bearing rods, all included in our 

 type F, could easily have induced authors like Migula and Matzushita to 

 create half a dozen "species" of that sort; perhaps this really happened. 



With the exception of D and H, all these types have been observed 

 and described in earlier publications on Azotobacter and closely related 



