CELLS OF BACILLUS MEGATHERIUM 61 



2 hours, so that the drawing of the two-hour sample serves to in- 

 dicate the character of the cells used for seeding. These were taken 

 from a rather old culture on dextrose agar. It will be observed that 

 three kinds of cells were present in the seeding, namely, spores, 

 sporangia, and cells of irregular form containing numerous granules. 

 As growth proceeded these all rapidly beca^me transformed into long 

 cylindrical cells, practically free of granules. The spores germinated 

 by simply gradually swelling and assuming elongated form. The 

 same thing happened to the irregular cells that were present in the 

 seeding, so that by six hours there were to be found only these long, 

 sausage-shaped, relatively hyaline cells. As growth proceeded these 

 long, clear cells became smaller and more and more filled with 

 granules. The number of spores present in the various samples was 

 somewhat irregular, probably due to variations in the distribution of 

 spores throughout the agar slant, as all of these preparations were 

 taken from the same agar slant. The large number of free spores 

 present, for instance in the twelve hour sample, were probably un- 

 germinated spores that had been present in the original seeding, and 

 there is no evidence of active spore formation again until after thirty- 

 six hours. By this time it will be noticed that all of the cells are 

 relatively small; the difference between the thirty-six and the six- 

 hour sample is, for instance, quite striking. With increasing age, 

 more and more spores develop within the cells, and the cells become 

 more and more irregular in form and filled with granules, until when 

 the culture is a week old we have nothing left but free spores and 

 bizarre, irregular, granular involution forms. Thus it will be seen 

 that at all stages there is a continuous and regular metamorphosis 

 taking place. 



For the present we will concern ourselves with the changes which 

 take place during the early stages of growth, with the development 

 of the large, clear cells characteristic of the active growth phase. 

 Variations in the size of the cell have been studied in micro-colonies 

 by continuous observation, and in a series of cultures on agar slants 

 and in broth, from samples removed at regular intervals of time dur- 

 ing growth. 



The micro-colonies were prepared by inoculating a loopful of 

 culture into a tube of molten agar. A loopful of this agar sus- 



