Resistance of Spores 23 



ing at one end, giving rise to club-shaped or drum-stick- 

 like cells, with the spores located at 'the extremity of 

 the thickened part. 



Vitality of spores. — The resistance of spores to ad- 

 verse conditions is very great. They are not destroyed 

 by drying, as are most of the ordinary bacterial cells, 

 and may retain their vitality while in a dried state, for 

 a long time. Well-authenticated instances are on record 

 when bacterial spores germinated years after they had 

 become dried out. When brought into liquids offering 

 suitable conditions, the spores begin to swell, and, 

 finally, burst open in one spot, giving rise to a new cell, 

 which then elongates, and multiplies in the normal 

 manner. Different species are not alike in their spore 

 germination. Aside from their resistance to drying, 

 bacterial spores can withstand other injurious con- 

 ditions, such as high temperatures, and the action of 

 destructive chemical agents. They are not destroyed 

 by boiling, hence, complete sterilization cannot be 

 effected simply by immersing the contaminated articles 

 in boiling water. 



Classes of bacteria. — Spore formation has been em- 

 ployed as a means of differentiation, and bacteria are, 

 therefore, classified as spore-forming and non-spore- 

 forming. A number of the well-known disease-producing, 

 or pathogenic organisms, Such as of typhoid, tuberculosis, 

 diphtheria, and cholera, do not produce spores in arti- 

 ficial cultures. This cannot, however, be accepted as 

 absolute proof that they produce no spores under any 

 circumstances whatever. 



Sterilization and pasteurization, — The formation or 



