WHAT ARE BACTERIA ? 35 



but by a process of fission, and as a result of the vegetative 

 division of the organism. It is quite possible, however, that 

 there is just as much differentiation of the protoplasm in 

 this case, as there is where the spore is formed within the 

 cell ; the only distinction being that the separation between 

 the spore and the vegetative element of the chain takes place 

 at an earlier stage, and more completely than in endosporous 

 reproduction. The reverse takes place, however, in the 

 Bacterium Zopfii, which during the vegetative or fission stage 

 consists of short rods, then of motionless filaments, and, if 

 the temperature be lowered from 30 C. to 25 C. of short 

 motile rods. As soon, however, as the conditions become 

 unfavourable, especially when the nutrient material in which 

 they are growing is exhausted, the rods, apparently, by a 

 simple process of fission are divided up into short roundish 

 cells, which retain their vitality for a considerable time, and 

 which, when again placed under favourable conditions, act 

 as spores, z>., they develop into the original characteristic 

 rod-shaped bacteria. 



In organisms in which spores are not found, the con- 

 ditions for their existence and propagation must always 

 remain favourable or they die out very rapidly, having no 

 specially resistant phase to enable them to tide over their 

 period of adversity ; and had we to deal with asporous 

 organisms only, they could, probably, by an organized 

 attack, be rapidly and completely exterminated. The vege- 

 tative organisms, as distinguished from their spores, cannot 

 survive the prolonged action of heat ; a comparatively 

 low temperature, 60 C. or less, being usually sufficient to 

 kill them, whilst the weaker chemical germicidal reagents 

 are quite sufficient to render them altogether innocuous 

 and inactive. The spores, on the other hand, can withstand 

 the action of a temperature anything short of 100 C. for a 

 considerable length of time. Cold and dessication have no 

 effect upon them, for after being submitted to any of these, 

 spores will, if placed under suitable conditions, develop into 

 the more characteristic vegetative forms. 



It must be borne in mind, however, that certain organisms 

 may, by careful acclimatization, be accustomed to exist and 

 even develop at extreme temperatures. Globig has shown that 

 certain bacteria found in the soil can only grow at a tempera- 

 ture of 50 C. or more, and that they can flourish up to 



