23 i Transactions of the Society. 



factor was the age or relative healthiness of the sheath. That is, 

 fresh sheaths growing freely in a pabulum of sulphuretted hydrogen 

 collapsed at once, but sheaths which had had very little sulphur- 

 etted hydrogen for twelve hours or so suffered less collapse, while 

 the sheaths which had been transferred to fresh water with very 

 little sulphuretted hydrogen, for twenty-four hours, rarely exhibited 

 collapse. 



The collapse is caused, therefore, by the mounting methods, 

 but depends on the " sulphur state " of the bacterial thread ; it 

 seems probable, therefore, that when the sheath is in exceptionally 

 favourable circumstances part of the sulphur is present in the 

 colloidal state in the cell, which, therefore, when surrounded by a 

 reagent of high osmotic pressure, will collapse ; when, however, 

 the cell is not so well supplied with sulphuretted hydrogen, the 

 colloidal sulphur in the cells changes to the granular form, and, as 

 a consequence, the cell becomes permeable to reagents, and so ex- 

 hibits no collapse. 



The author's reason for making this small communication is 

 that stream-growths are frequently identified from stained prepara- 

 tions which, on occasion, as can be seen from the slides, would 

 certainly lead to Bcggiatoa being described as Sphserotilus. 

 Growths of higher Bacteria should invariably be identified, 

 unstained and untreated in anyway, in a film of water illuminated 

 with a dark-ground illuminator. 



A point which the author would like to raise for discussion is 

 why the sulphur granules in the sheaths have not reverted to 

 a-sulphur, a change which, as Winogradsky describes, takes place in 

 forty-eight hours in sheaths killed in dilute picric-acid solution, 

 but which receive no further treatment. 



The dye used in making the preparations for these slides was 

 gentian- violet in alcoholic or anilin solution. 



The negatives were made in a vertical camera by Nachet, the 

 optical equipment being a 2 mm. semi-apochromat N. A. 1 • 32 by 

 Leitz and a X4 complanat eye-piece by Winkel ; illumination was 

 effected by a Thoria composition " lime " heated by oxygen and 

 coal gas, the light being filtered by a copper-sulphate and picric- 



EXPLANATION OP PLATE VII. 



Fig. 5. — Strand of Beggiatoa alba ( x 750). Collapse and disappearance of sheath. 



From infusion. 

 ,, 6. — Strand of Beggiatoa (x 1000). Collapse ; no granulation visible ; collapse 



of sheath in places ; cell-material collapsed in one place to a thread 



with slight bulging of sheath. From infusion. 

 „ 7. — Strand of Beggiatoa alba (x 750). Collapse and granulation of cells; 



very visible distortion of the collapsed cells has also taken place ; the 



sheath is nearly invisible, but is outlined against the other bacteria 



present. From infusion. 



