326 The Microscope. 



pvire, but the prevailing organism was a Bacillus of apparently the 

 same microscopical and culture characteristics as that found the year 

 before. This organism was easily obtained in a state of purity by 

 plate cultures, and also was found to be pure in several direct trans- 

 fers from the old stalk, care being taken to efPect this result. 



The inoculation experiments upon the yoang plants wei'e at 

 once successful both from macerations of the old diseased stalk, and 

 from pure cultures of the Bacillus mentioned. Checks were made 

 upon the same or similar plants by the use of sterilized- water, and of 

 sterilized beef-broth, like that in which the cultures were made. 

 Studies were prosecuted until the first of June, when they were 

 again interrupted, to be resumed a month later. 



Without pausing now for the records of single experiments, a 

 general summary of results is presented. 



In the described disease of broom-corn and sorghum, a specific 

 Bacillus is constantly found in the affected tissues, both of the roots 

 and of the aerial parts of the plants. Pure cultures of this Bacillus 

 may be made in beef -broth, and in infusions of potatoes, and of 

 maize kernels, as well as upon nutrient gelatine and agar agar. The 

 best growth takes place at a temperatvire of about 36° to 37° C, but 

 development proceeds more slowly, as the temperature is reduced 

 below 2b'^ C. Still lower temperatures were not tested. In potato 

 infusion, in a test-tube, inoculated with a minute amount of a pre- 

 vious culture or directly from the diseased tissues, and placed in 

 incubator at 36'"°' C, the limpid iluid becomes sensibly turbid in 

 twelve hours, and in twenty-foitr hours conspicuously so. In the latter 

 case, spores may be sparingly found. These are produced in a char- 

 acteristic and uniform manner, one in the middle of each cylindi'ical 

 segment of a chain, or in the individual microbe if separated. 

 There is some iindetermined condition under which the chains of 

 cohering organisms are formed, for in some cases this is the pre- 

 vailing form, while in others, apparently similar, the individuals are 

 separated. In the most active stage of growth — say at twelve houi's 

 under the above conditions — the organisms are almost uniformly in 

 pairs. In the preparation for spore-formation changes take place 

 in the protoplasmic contents of the cells, indicated by the action of 

 staining agents. During active growth, methyl-violet stains, uni- 

 formly and deeply, the whole body. When spore-formation begins, 

 the central area of each cell is noticeably paler. At first, this lighter 

 colored portion looks like a pale indistinct equatorial band or zone 

 without distinct limitations. Gradually the differentiation becomes 



