Changes of nuclear structure in bacteria have been studied by means of the hydrochloric acid-Giemsa method which produces brilliantly stained specimens and can be carried out with almost the same ease as some of the ordinary routine staining techniques.

The nuclear changes in the four spore-bearing organisms studied are outlined in Text-fig. III, to which the following numbers refer. The dumbbell bodies which are dispersed in the cells of the young growth (1) become alined in the long axis of the cell (2) where they eventually fuse into an axial nuclear cylinder (3, 4). These cells divide up into fusion cells of approximately the same length (5). The development of the ‘chromosome’ stage (1) into the fusion cell (5) is the first step in the process of sporulation. During its further development the fusion cell or spore mother cell divides twice (6, 7), with the result that it is segregated into four structures which often assume dumbbell shape. Therefore the chromatin cylinder of the individual spore mother cell seems to be equivalent to four nuclear elements one of which functions as the spore ‘chromosome’ (‘nucleus’?), whereas the remaining three disintegrate (8, 9). The ripe spore (9) representing, as it does, the smallest cell unit contains one nuclear structure only.

Therefore the two main features in spore formation of bacteria appear to be (1) a fusion of the dumbbell bodies into an axial chromatin rod (‘autogamy’?), (2) a reduction partition which is reminiscent of, though not corresponding to, the more complicated phenomenon of meiosis in the higher organisms. The sporulation, as outlined in this paper, gives new proof of the important part played by the chromatinic dumbbell bodies (‘chromosomes’) in the developmental cycle of spore-bearing organisms. The fusion cell with its axial chromatin cylinder has for the first time been proved to have a progressive functional significance as a stage in a nuclear cycle. The particular mode of fusion followed by reduction partition suggests that the chromatinic dumbbell bodies may be concerned with the transmission of the hereditary characters in bacteria.