404 Hillhousia mirabilis, a Giant Sulphur Bacterium. 



cilia. It occurs among decaying organic matter in the mud of shallow fresh- 

 water pools. 



Each individual contains a protoplasmic network in the wide meshes of 

 which large globules of sulphur (probably not pure, but in loose combination 

 with proteid material), are located. The network includes numerous small 

 granules, a considerable proportion of which consist of some nucleo-proteid. 

 None of them are chromatin granules. 



The cell-wall is firm and has great powers of resistance to reagents. It is 

 not homogeneous, and 5-per-cent. carbolic acid demonstrates its lamellose 

 character. 



The multiplication of the organism is relatively slow, one division 

 occupying upwards of 24 hours. 



EXPLANATION OF PLATE. 

 Figs. 1—16, each X 500 ; Figs. 17—21, each x 1000. 



Figs. 1 — 3. — Drawings of living specimens of Hillhousia mirabilis to show the dark 

 refractive sulphur globules practically filling the whole cell. 



Fig. 4. — Specimen kept in tap water for one week. The sulphur globules have been 

 almost entirely used up in respiration. 



Fig. 5. — Individual after being in a 2^-per-cent. solution of commercial formalin for 

 several days. The sulphur is completely removed and the protoplasmic net- 

 work becomes very obvious. Note the numerous granules in the network. 



Fig. 6. — Outline of a curved cell. These are rarely observed, the great majority of the 

 cells being straight. 



Figs. 7 — 9. — Outline of three distinct specimens showing three of the principal stages in 

 simple cell-fission. In fig. 9 the constriction is almost complete. 



Figs. 10, 11. — Two individuals after treatment for 14 days with 10-per-cent. NaCl. 



Many of the granules in the network have been removed, and there is a 

 decided contraction or shrinking of the central parts of the network. 



Fig. 12. — Individual after prolonged treatment with 2-per-cent. KOH. The protoplasmic 

 network is largely disorganised, and a large number of the granules have been 

 dissolved. 



Figs. 13, 14. — Two cells after treatment for about 15 minutes with 5-per-cent. carbolic 

 acid. The cell-wall exhibits a lamellation, and the sulphur globules have 

 coalesced into a central irregular mass. 



Figs. 15, 16. — Two cells immediately on treatment with 40-per-cent. commercial 

 formalin. The numerous short cilia are very readily observed for a brief 

 period, and many of them can be seen to be thrown off into the surrounding 

 liquid. 



Fig. 17. — Isolated sulphur globules, showing their irregular form, obtained by crushing 

 the living cell. 



Fig. 18.— Small crystals (rhombic prisms and rhombohedra) of sulphur obtained by 

 allowing the living organisms to completely dry up. These crystals are 

 formed outside the organisms, the colloidal sulphur passing through the cell- 

 wall to the outside after irrigating with water. 



