THE LEUCO-THIOBACTERIA 97 



protoplast segments into a number of equal or approximately 

 equal lengths, and that the morphological changes outlined 

 above take place in a regular sequence. Autolysis must be 

 regarded as a vital phenomenon, as much so as the capacity 

 of a plant to respond to such outside influences as light, 

 gravity, etc. In the course of this response ferments may or 



Fig. 6. — Beggiatoa alba (Vaucher). Trevisan (i), 1842. 

 a. — Photomicrograph (shghtly touched up) of a short filament containing 



a few granules of sulphur. x 1200. 

 b.- — Fragment of thread undergomg autolysis. Transverse walls are clearly 

 visible. At one point the protoplast has receded from both sides of the 

 transverse band of sheath (at b) leaving a clear space. This manner of 

 separation is characteristic of the process. X 1500. 

 c. — Shows the first stage in autolysis. The thread has broken up into 



fragments of approximately equal lengths. x 1500. 

 d. — Second stage in autolysis. Transverse bands of hardened slime are 



seen between the segments. x 2000. 

 e. — Third and final stage in autolysis. Nine segments are shown, of which 

 three are in process of swelling, preparatory to dissolution, x 1500. 

 (For further explanation see text.) 

 /. — Short filament with four endospores. x 1500. 

 e — Endospore. 



s — Sulphur globule, somewhat contracted, lying in its vacuole. 

 g. — Semi-diagrammatic representation of a portion of thread to show 

 alveolar arrangement of the plasma. x 4500. 

 V — Vacuole, 

 s — Sulphur globules. 

 g — Minute granules in plasma. 

 h. — Filament in last stage of autolysis. Whilst the sheath has remained 

 comparatively unchanged, its contents have almost disappeared. 

 X 1500. (For further information see text.) 

 c — Rerhains of the disappearing segments. 

 sh — Sheath. 



b — Transverse band of sheath-material. 



d — Debris left after disappearance of another portion of the 

 filament. 



may not be developed, but if formed they are to be regarded 

 as concurrent, not as causative agents in the production of the 

 phenomenon, and their presence as an incidental, not as a 

 necessary feature. 



The mechanism of the process is a physical one. All 

 living cells contain osmotically active substances, and normally, 

 equilibrium is maintained because the outward pressure is 



7 



