50 Upon the Action of Gravity on Bacterium Zopfii. [Feb. 23, 



and coccal forms predominate ; there appears to be an absence cf the 

 motile spiral form. In the motile phase there is a very slight lique- 

 faction of the gelatine, but for the rest there is no liquefaction 

 of the gelatine. In addition to the differences of form of the 

 separate elements, there appear certain phases in the grouping of the 

 bacteria. Thus, following Billet, we divide our growths into 

 filamentous, disassociated, skein, and zoo gleaf or m phases. The filament- 

 ous form is especially met with in gelatine, and in the pinnate growths 

 the filaments are at first very long and hyphal-like, and are rapidly 

 growing, but segmentation follows early. If branching occurs it 

 appears to take place as in Gladothrix, by displacement of segments. 

 In the disassociated phase the segments break away from one another, 

 and may become motile. The skein phase is met with on hard gelatine 

 and on agar ; it is a very superficial growth, and the filaments form 

 dense plaits ; it is not met with in geotropic growths. The 

 zoogleaform phase is very characteristic, and usually rapidly follows 

 upon the filamentous. In the filaments and segments multiplication 

 occurs either at scattered points in the chain or throughout its 

 length, and the segments remain united by a common cementing 

 substance ; the forms assumed by these aggregates are very beautiful, 

 and are to be met with in the geotropic growths. 



The Spirillation. — The undivided or segmented filaments and the 

 zoogleaform masses have a marked tendency to twist, especially in 

 the pinnate gelatine cultures. The majority of the twists are in the 

 opposite direction of the hands of the clock. Kurth noted the 

 spirillation, and attributed it to the resistance of the gelatine; 

 but as in the higher plants, perhaps here, the action of gravity is 

 also a factor. This consideration also opens up the meaning of the 

 spiral form in the bacteria. 



Methods of Fixing and Staining employed. — Our preparations, from 

 which the micro-photos were taken were obtained from plate cultures 

 made in the following manner : — A micro-slide in a large sterilised 

 test tube is coated with a thin surface of sterilised gelatine by means 

 of a balloon pipette. After solidification the surface is inoculated 

 with a streak. The growth may be examined either unstained or 

 after fixing and staining. To fix, the slide is withdrawn from the 

 test-tube and placed in dilute alcohol, and then dried ; any stain can 

 then be employed, and the preparation mounted in Canada balsam. 



