434 r. CLIFFORD DOBFLL. 



spiral filament — succeed one another at different times in the- 

 life-cycle. But I will reserve a discussion of this for another 

 part of the paper (see p. 481). 



(li) Bacilli of the spirogyra Type. 



Under this heading I will describe those Bacilli whiclb- 

 possess a structure like that of Bacillus spirogyra. I have 

 encountered many Bacteria of tins form, and believe the type 

 of organisation which they display to be a very common one. 



(1) Bacillus spirogyra. — I have already given a full 

 account (Dobell, 1909) of the structure and life-hi.story of 

 this Bacillus, which occurs in the large intestine of Rana 

 temporaria and Bufo vulgaris. My published figures 

 are all of organisms fixed with formalin and stained witK 

 Giemsa. As this method involves drying before mounting 

 (see p. 415), I have thought it advisable to publish a few 

 more figures of the organism after treatment by a more- 

 approved method, though — as I have pointed out on p. 416 — 

 drying after fixation with osmic acid or formalin does not 

 appreciably affect the appearance of the cells as a rule. 



Figs. 117 and 118 (PL 18) are accurate drawings of, 

 Bacillus spirogyra fixed with corrosive sublimate and 

 acetic acid and stained with Heidenhain's iron-htematoxyliu. 

 No drying was allowed to take place at any stage during the 

 making of the preparation — a moist film cover-glass prepara- 

 tion of the undiluted contents of the large intestine of a toad 

 (B. vulgaris). It is very difiicultto obtain good preparations 

 of this organism with iron-htematoxylin, on account of the 

 strong affinity of the pellicle for the stain. During* differen- 

 tiation the nuclear filament and the pellicle give up the stain 

 at almost the same rate, so that one is a])t to over-differentiate. 

 But when differentiation has been stopped at exactly the- 

 right moment, very distinct figures of the cell-structure can. 

 be obtained. 



The appearances presented by the cells after this method, 

 of treatment are essentially the same as those obtained by. 



