THE LEUCO^THIOBACTERIA 119 



Marked differences in size are noted in this organism : — 



Schewiakoff . . . I5/^ X 9 — •22/x. 



Frenzel .... 9 — ■I5ju, X 6 — -33ju.. 



West and Griffiths . . 40 — 60ju X 20 — ^},yL.. 



Nadson .... Up to I02/Lt in length. 



The smallest appears to have been that recorded by Baven- 

 damm, which was only 3/x in length. 



Achronialiuni supplies another illustration of the fact 

 that all widely distributed bacteria exhibit a wide range of 

 dimensions, and that within the extremes of this ran^e are 



Fig. 14. — HiUhousia. (West and Griffiths.) 

 A. — Normal aspect of living specimen of HiUhousia niirahilis. X 500. 



The cell is filled with globules of calcium carbonate. 

 B. — H. mirabilis after removal of calcium carbonate by dilute acetic 



acid. The conspicuous granules are grains of sulphur, x 850. 

 c. — Rhombic crystals of calcite, obtained by allowing the organism to dry, 



and then irrigating with distilled water. X 850. 

 D. — After treatment for 15 minutes with 5 per cent, phenol. Shows lamel- 



lose cell wall. 

 E. — Diagrammatic representation of two stages in the division of H. 



mirabilis. 

 F. — Cell after removal of cell contents. 

 G. — Photomicrograph of H. mirabilis from material kindly sent to the 



author by Dr. B. M. Griffiths. X 450. 

 a-f are taken from West and Griffiths' paper (see Bibliography). 



a multitude of intermediate forms. Hence one specific name 

 should cover all that fall within the range. A new specific 

 name is called for on the score of differences in size only when 

 a distinct gap occurs in the grading. In plastic organisms like 

 the sulphur bacteria, a variation in the size of the different 

 individuals in a culture has no more genetic significance than 

 the variation of the number of sulphur globules in the cells. 



Methods of Reproduction. 



(A) Fission. — Two stages in division arc shown diagram- 

 matically in Fig. 14E. This process has not been followed 

 in detail. 



