RESISTING POWER OF THE ENDOSPORES. 65 



named Bacillus pseud-anthracis, that spore formation was influenced 

 favourably by violet light but unfavourably by red light. 



Past experience has shown that the formation of endogenous 

 spores is confined to the rod-shaped species (bacilli). This observa- 

 tion has been utilised in the classification of bacteria, as will be 

 seen in 69. The reports to the contrary found in the literature 

 of the subject lack the force of proof, since they ignore the fact 

 that the sporous nature of the growths seen to originate in the 

 cocci has been demonstrated by germination tests. 



53. Resisting- Power of the Endospores. 



The forms in question are endowed with the character of re- 

 productive cells, since they are able to withstand those adverse 

 conditions which would inevitably be fatal to the vegetative forms. 

 As in the following sections especially that dealing with sterilisa- 

 tion occasion will often arise for a closer investigation of this 

 faculty, so important for the maintenance of the individual species, 

 an exhaustive and tedious list of individual cases need not be 

 given here ; it will therefore suffice if we cite one example, viz., 

 Bacillus subtilis. According to the researches of BREFBLD (I.), 

 which were confirmed by M. GRUBER (L), a continuous exposure of 

 twenty minutes to the action of boiling water suffices to destroy 

 the sporeless rods of this microbe ; whereas to kill the spores 

 requires three hours' boiling at 100 C., or a quarter of an hour's 

 exposure at 105 C., or, finally, the action of a temperature of 110 

 C. during five minutes. The assertion made by Koch, that the 

 continuous action of steam at 100 C. for fifteen minutes will 

 destroy the spores of any of the bacteria, was subsequently 

 negatived by his pupil E. VON ESMARCH (II.). According to 

 SWAN (I.), spores of Bacillus megatherium, dried on a cover-glass, 

 retained their vitality and germinating power for more than three 

 years. 



Use may be made of these powers of resistance for separating 

 the sporiferous from associated non-sporiferous bacteria. By skil- 

 ful handling, e.g. by the aid of sufficiently high temperatures, 

 the weaker species in a mixture of bacteria can be killed off, 

 leaving only the spore-producing individuals. A process based 

 on this mode of procedure, and known as the boiling method, 

 was introduced into bacteriology by ROBERTS (I.) for obtaining 

 pure cultures of the hay bacillus, and the same method was 

 employed by Prazmowski for preparing cultures of Clostridium 

 butyricum. 



The seat of this high power of resistance has already formed 

 the object of numerous researches. One school looks for it in a 

 peculiar modification of the spore plasma for instance, in the pre- 

 sumably low water-content thereof, as suggested by LEWITH (I.). 

 Others, again, attribute to the spore membrane an exceptionally 

 VOL. i. E 



