98 SULPHUR BACTERIA 



balanced by the resistance of the somewhat hardened and 

 chemically changed outermost layers of the protoplast. The 

 balance is evidently a very delicate one, and one which is 

 easily destroyed by a further change in the constitution of 

 the resisting outer layers when these are transformed into 

 slime. This causes the outwardly directed pressure to over- 

 come the resistance of the outer layers, with the results described 

 above. It is as though the leather casing of an inflated foot- 

 ball were gradually changed into a softer material. Expansion 

 would occur and ultim.ately there would be a complete dis- 

 appearance of the ball. A hypothetical ferment may be pre- 

 dicated to bring about the transformation of the outermost 

 layers, but there is no necessity to assume its existence to 

 explain what in the last resource is a vital phenomenon, which 

 does not necessarily demand the existence of a ferment for 

 its manifestation. 



Methods of Reproduction. 



(A) Fission.~T\\e normal method of reproduction is by 

 fission. At first the two daughter cells are attached by a 

 band of slime continuous with the surface slime. This is made 

 clearer on staining the slime with iodine or carbol-fuchsin. 

 Later the daughter cells gradually draw apart, but the contin- 

 uity of the slime is maintained until the cells are about their 

 own length apart. 



Zopf (2) states that the separation is facilitated in station- 

 ary threads by the swinging movements of the free end, and 

 Winogradsky (2) affirms that a break usually occurs at a place 

 on the thread where a large vacuole is found. 



(B) Endospores. — Structures similar to endospores were 

 observed on one occasion inside the threads of a Beggiatoa 

 growing in a pool on the rocks near the Millport Marine Bio- 

 logical Station, Scotland. 



The following reasons suggest that these structures were 

 spores : — 



[a) Constancy of size and shape (4/Lt long and 3-5/x broad). 

 [h) Difiiculty of staining. 



