32 BACTERIA AND SOIL FERTILITY 



Spore Formation. — When adverse conditions arise many 

 bacteria mobilize the vital parts of their body into much smaller 

 space than they occupy during their normal life. They exclude 

 all of the excess moisture and surround themselves by a tough 

 resistant coat. In some respects this form of the organism re- 

 sembles the seed of the higher plants, and we speak of it as the 

 spore. While in this stage they will Withstand many conditions 

 which would quickly prove fatal to the growing bacteria. Some 

 of them, while in this condition, can withstand the temperature 



of boiling water for 

 i% * M 2 Q -. Q ^ many hours, or they mav 



I I' $.^ i ^' 



^^ ^^^ ^ with strong carbolic acid. 



P'or the time being they 

 have lost the power of 

 multiplying, but they are 

 still alive, and if they are 



Fig. 17. — ^Types of spoiangia and spores m 1 • • 



bacteria, i, a sphillum with a terminal en- brought into appropriate 



laiged spore. 2, bacillus with a terminal surrOUndingS they will 



enlarged spore. 3, bacillus with teimmal . 1 u 



spore, not enlaiged. 4, bacillus with an Change intO* normal bac- 



equatorial spore, not enlarged. 5, baciUus ^^j-j^ j^g^ ^g J^^g ^j^g ]^gj.„ 

 with two small terminal spores. 6, bacillus 



with two elongate spores. 7, 8, bacilli nel of wheat change into 



with equatorial swollen spoies, Clostridia ^1 i x. i. 



(after Buchanan). ^^^ 7^^^^^ Pl^"^^ when 



placed in moist soil. 

 It is indeed fortunate for mankind that but few of the disease- 

 producing organisms form spores. There are, however, many of 

 the bacteria which cause fruit, meat, and various other food prod- 

 ucts to spoil, which do form very resistant spores, and this is why 

 many food products have to be heated for such a long time or to 

 such a high temperature to make them keep. At times, in order 

 to avoid heating the substances to such a high temperature, the 

 intermittent method of sterilization is made use of. In this 

 method the substance which is to be sterilized is heated to 100° C. 

 for a short time. This heating kills all of the organisms which 

 are not in the spore form. After standing in a moderately warm 

 place for twenty-four hours, during which time the spores start 



