602 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Drilosiphon and Leptoihrix, from which, in certain circumstances, 

 bacteria are produced. The filaments of Leptothrix muralis, which is 

 very common in greenhouses, forming a gelatinous deposit on the 

 walls, are usually of a light yellow colour ; but when, as is frequently 

 the case, they grow among the stems and leaves of mosses, they 

 gradually become green. It must therefore be assumed that there is 

 always in this species of Leptothrix a certain amount of green 

 colouring matter, — another illustration of the difficulty of drawing 

 an exact line of demarcation between the Schizomycetes and the 

 Schizophyce^. It agrees with ordinary Schizomycetes in the capacity 

 for assuming bacterium, bacilltis, coccus, and vibrio-forms ; and this 

 sometimes takes place even with filaments which are distinctly 

 green. 



When a piece of pure leptothrix-jelly is cultivated under water 

 in a glass cell, hormogonia are soon separated, the time of their 

 appearance depending on the temperature of the water. These either 

 again develope into filaments, or pass into the bacterium form or, 

 finally, into the swarming condition. It is usually only the outside 

 filaments which project from the jelly that develope into hormogonia, 

 which either break through the mucilaginous sheath or escape through 

 its open end ; on their escape they frequently display movements of 

 circumnutation, due to the contraction of the protoplasm and not 

 to the presence of cilia ; the vibrio-form appears, however, to 

 possess cilia, though the author was not able to determine their 

 presence with certainty. The vibrio-form is developed only from a 

 few of the filaments at the margin of the jelly, presenting thus 

 a striking contrast to the true Schizomycetes, in which both the 

 vibrio and spirillum form-appear suddenly in large quantities, The 

 bacterium form of L. muralis exhibits an evident segmentation, espe- 

 cially after the application of dilute hydrochloric acid or potassium 

 acetate. The hormogonia, when they do not grow into filaments, 

 usually break up into bacteria, which then excrete a thick gelatinous 

 envelope, and swim on the surface of the culture-fluid, a zoogloea 

 family being slowly formed in this way. Less often the bacillus and 

 spirillum forms develope zoogloea colonies. Occasionally, by cell- 

 division within the jelly, the zoogloea acquires the habit of a palmella 

 or merismopsedia. 



The presence of phycochrome is indicated by the motile hormo- 

 gonia always collecting on the illuminated side of the vessel. Under 

 certain conditions the bacteria swarm out of the zoogloea-jelly, leaving 

 their membrane behind; the cell-contents arrange themselves in a 

 direction at right angles to the original one, and may develope into 

 the bacillus, leptothrix, or spirillum form, then dividing into bacteria, 

 &c. ; but in all the forms the representatives of the last generation 

 are always smaller than the preceding one, finally reaching the limits 

 of vision with the best immersion system. 



In addition to the forms above described, Leptothrix muralis much 

 less often developes cocci, arranged in a moniliform string, often 

 interrupted by a large strongly refringent cell. Filaments are some- 

 times found which are segmented above into cocci, below into bacteria. 



