6 GENERAL MORPHOLOGY AND BIOLOGY. 



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 I 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 transversely. In 

 the last case the dehiscence may be partial, and the new indi- 

 vidual 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 



