[Jones] STUDY OF SOME AZOTOBACTER 61 



are found projecting from any part of the body are most common at 

 the poles, and vary in number from one to five or more. With the A4 

 variety, polar tufts of flagella are common. 



Moist Chamber Cultures. 



Many moist chamber cultures were prepared in the ordinary way 

 without any growth occurring in them. After further attempts had 

 been made in which the conditions were changed, it was eventually 

 found that lack of aeration in the ordinary moist chamber was the 

 inhibiting factor. To overcome this difficulty, cell rings with an inter- 

 ior diameter of one inch and cover glasses 1% inch wide by 2^ inches 

 long were used. The cover slip with the prepared culture on it was 

 placed over the cell and fixed there, leaving a space of ^V inch between 

 the edges of the cover slip and the inside wall of the cell ring on each of 

 two sides. This gave ample aeration and when loss of moisture occurred 

 by evaporation or in any other way, it could be made good by adding 

 sterile water with a fine pointed pipette. In such moist chambers 

 growth occurs readily, and the development of a colony from an indi- 

 vidual cell can be witnessed through the oil immersion lens. Photo- 

 micrographs of such colonies were taken as they were developing. 

 See PI. IV. When moist chambers are made from cultures from one 

 to ten days old, the majority of the cells used for innoculation produce 

 colonies. When the inoculating material is taken from older cultures 

 there is a percentage of cells which do not reproduce, the percentage 

 of such increasing with the age of the culture. Young cells begin to 

 reproduce in four or five hours, older cells do not show signs of germina- 

 ting for several days. In the case of young cells where the interna! 

 plasma is homogeneous, there is simple elongation of the cell followed 

 by fission. Frequently, the aforementioned supposed nuclear body 

 is present and sometimes it can be seen to divide at the same time as 

 the cell — fission of the two being in the same plane and simultaneous. 

 See PI. IV, Figs. 1 and 2. If the inoculating cells are old and granular, 

 multiplication, when it does take place, is a phenomenon something 

 like the germination of a spore. The cell membrane appears in some 

 cases to rupture and from amongst the granular mass homogeneous 

 protoplasm encased in a thin membrane emerges and a short thick 

 rod develops. At other times, the cell enlarges, granules of the No. 1 

 type which may be closely packed together practically filling the cell 

 will be slowly pushed apart, and fission of the cell ensues, each of the 

 daughter cells retaining some of the granules. See PL III, Fig. 7. As 

 multiplication continues, these granules sometimes disappear as though 

 they are used up by the cell activities, until when the colony consists of 



