482 C. CLIFFORD DOBELL. 



all stages in the life histoiy. This point seems to me worth 

 special attention. 



In the case of Bacillus saccobranchi,! have pointed 

 oat that the nucleus may be in the form of a spiral filament, 

 oi' in the form of chromidia, or in forms intermediate between 

 these and characterised by having- an appearance of irregular 

 strands, granules or networks of chromatin. There can be 

 no doubt that, in this Bacillus at least, the nucleus has a 

 variable structure. There is, however, no evidence to show 

 "what relations these various nuclear modifications bear to the 

 life-cycle as a whole. All that can be said at present is that 

 these different nuclear forms exist. 



When we turn to the Bacilli of the flex ills type, however, 

 we have exact knowledge of the relations between the nuclear 

 modifications and the phases in the life-cycle. From 

 Schaudinn's (1902) study of B. biitschlii and my own re- 

 searches on B. flexilis and allied forms it can be definitely 

 stated that the chromidial stage represents the normal 

 vegetative condition of the nucleus, existing throughout the 

 greater part of life. A nucleus in the form of a spiral 

 filament occurs as a transient stage connected with, and 

 immediately preceding, spore-formation. In the spore itself 

 a third nuclear modification is seen. The chromatin is in the 

 form of a densely aggregated mass, which constitutes the 

 chief part of the living substance of the spore. From this 

 aggregated mass the chromidial condition is again assumed 

 in the process of germination from the spore. 



In the Bacilli which I have termed those of a "modified 

 flexilis form,'' these three nuclear conditions are encountered 

 in a modified form, but their relation to the phases of the 

 life-cycle has not been determined. 



In Spirillum monospora (Dobell, 1008), Bacillus 

 sporonema (Schaudinn, 1903) and many other Bacilli 

 (Gruilliermond, 1908) only two modifications of the nucleus 

 have been established. During the vegetative condition the 

 nucleus is in the form of chromidia. It then assumes the 

 form of an aggregated mass, which enters into the formation 



