26 MORPHOLOGY 



cytoplasm between the central cytoplasmic core and the spore membrane, and 

 considers that this, rather than the spore membrane itself, is responsible for the 

 refractility commonly seen in unstained preparations of spores. 



Most of the available evidence indicates that the spore is simply a resting 

 stage of the bacterial cell, in which it is far more resistant to adverse environ- 

 mental conditions than it is in the ordinary vegetative form. The spores of 

 bacteria of the Bacillus group have a bound water content of the order of 60-70 

 per cent., as compared with 3-21 per cent, in the vegetative cell (Henry and 

 Friedman 1937, Friedman and Henry 1938). By spectrochemical analysis 

 Curran, Brunstetter and Myers (1943) found that the spores contained substantially 

 more Ca, more Cu and Mn, but less P and K than the vegetative cell. They 

 suggest that heat resistance is associated with, though not necessarily immediately 

 dependent on, high bound water and Ca content of the spore. The protoplasm 

 of the spore differs materially from that of the vegetable cell ; both Howie and 

 Cruickshank (1940) and Lamanna (1940) have demonstrated the antigenic dis- 

 similarity of spores and their parent vegetative forms (see Chapter 8). 



Fig. 9. — The cell wall of B. megatherium after plasmolysis, showing transverse septa, 



both complete and incomplete ( X 3,500). 



(From a photograph kindly supplied by Dr. C. F. Robinow.) 



The resting spore retains its capacity to germinate for long periods. Graham- 

 Smith (1941), for example, noted the survival for over seventeen years of the dry 

 spores of B. anthracis kept in diffuse daylight at room temperature, while Wilson 

 and Shipp (1938) were able to grow sporing bacilli from preserved meats that 

 had been sealed in containers for 114 years. 



There is little evidence that spore-formation is associated with any sexual 

 reproductive process. Certain appearances which have been interpreted in this 

 sense by Schaudinn (1902), and Ruzicka (1909), have been shown by Dobell (1911) 

 to have no such significance. 



However, from their careful studies of the nuclear structure of a spore-bearing bacillus 

 (see above) Allen, Appleby and Wolf (1939) concluded that the spore was not a resting 

 stage, but provided an opportunity for a re-arrangement of nuclear material. In this 

 connection it is noteworthy that Kaplan and Williams (1941), aft.er exploring the cultural 

 conditions which induced spore formation in CI. sporogenes, concluded that sjjore-formaiion 

 was a natural phenomenon in the developmental cycle of the organism. Klieneberger 

 (personal communication) has observed in several species of Clostridia a process in which 

 the dumbbell chromatinic bodies present in filamentous forms of the bacteria join into 

 axial structiu"es ; these then divide into four chromatinic bodies, one of which matures into 

 the nuclear body of the spore, while the remaining three disintegrate. The process 

 suggests a form of autogamy, and that the spore is more than a resting stage in the life 

 history of the bacillus. 



