6 GENERAL MORPHOLOGY AND BIOLOGY 



short distance from one extremity (Fig. 1, s). In structure 

 the spore consists of a mass of protoplasm surrounded by a dense 

 membrane. This can be demonstrated by methods' which will 

 be described, the underlying principle of which is the prolonged 

 application of a powerful stain. The membrane is supposed to 

 confer on the spore its characteristic feature, namely, great 

 capacity of resistance to external influences such as heat or 

 noxious chemicals. Koch, for instance, in one series of experi- 

 ments, found that while the bacillus anthracis in the unspored 

 form was killed by a two minutes' exposure to 1 per cent, carbolic 

 acid, spores of the same organism resisted an exposure of from 

 one to fifteen days. 



When a spore is placed in suitable surroundings for growth, 

 it again assumes the original bacillary or spiral form. The 

 capsule dehisces either longitudinally, or terminally, or trans- 

 versely. In the last case the dehiscence may be partial, and the 

 new individual may remain for a time attached by its ends to 

 the hinged spore -case, or the dehiscence may be complete and 

 the bacillus grow with a cap at each end consisting of half the 

 spore-case. Sometimes the spore-case does not dehisce, but is 

 simply absorbed by the developing bacterium. 



It is important to note that, in the bacteria, spore formation 

 is rarely, if ever, to be considered as a method of multiplication. 

 In at least the great majority of cases only one spore is formed 

 from one bacterium, and only one bacterium in the first instance 

 from one spore. Sporulation is to be looked upon as a resting 

 stage of a bacterium, and is to be contrasted with the stage 

 when active multiplication takes place. The latter is usually 

 referred to as the vegetative stage of the bacterium. Regarding 

 the signification of spore formation in bacteria, there has been 

 some difference of opinion. According to one view, it may be 

 regarded as representing the highest stage in the vital activity 

 of a bacterium. There is thus an alternation between the 

 vegetative and spore stage, the occurrence of the latter being 

 necessary to the maintenance of the species in its greatest 

 vitality. Such a rejuvenescence, as it were, through sporulation, 

 is known in many algae. In support of this view there are 

 certain facts. In many cases, for instance, spore formation only 

 occurs at temperatures specially favourable for growth and 

 multiplication. There is often a temperature below which, 

 while vegetative growth still takes place, sporulation will not 

 occur ; and in the case of b. anthracis, if the organism be kept 

 at a temperature above the limit at which it grows best, not 

 only are no spores formed, but the strain may lose the power 



