Effects of Bacterial Growth on the Environment 175 



heat is dissipated before it has an opportvmity to build up to a 

 measurable degree, the exothermic reactions are not usualK ob- 

 served. Grain and vegetable cells during their metabolism can 

 add heat to that produced when the moisture content is sufficiently 

 high to support microbial growth. Spontaneous combustion of 

 haystacks can be attributed to an initial build-up of heat by these 

 metabolic processes, and when the temperature reaches a certain 

 level, purely chemical reactions may step in and spark the ignition. 



As early as 1884, Schloesing claimed that the heating of hay- 

 stacks and manure piles was a combination of the work of organ- 

 isms and chemical oxidation. He held that bacteria are the major 

 cause of temperatures up to 70° C, and from this point upward 

 chemical processes carry on the thermal reaction. Ferdinand 

 Cohn (1888) remarked that temperatures up to 35° C. are due 

 to plant cell respiration, and that heating from 35° C. to 45° C. 

 is brought about by molds. It was reported by Rabinowitsch 

 ( 1896 ) that thermophiles develop rapidly after an initial heating 

 process, and these organisms cause an increase in ammonia which 

 facilitates the heating of manure. Distillation products mixed with 

 the air, according to Laupper in 1927, produce a detonating gas 

 which is the immediate cause of spontaneous combustion in the 

 presence of pyrophoric iron. 



In a study of the heat produced in grains by single pure 

 cultures of organisms as well as by mixed cultures, James, Rettger, 

 and Thom (1928), and later Wedberg and Rettger (1941) devised 

 insulated chambers with automatic aerating devices. By employ- 

 ing cracked corn as a substrate and by adjusting the moisture 

 content to about 30%, temperatures as high as 67° C. were recorded 

 with mixed cultures, and close to 60° C. was registered with a pure 

 culture of Bacillus subtilis growing on sterile cracked corn. This 

 organism is also popularly known as the hay bacillus. Temperature 

 values of between 45° C. and 55° C. were quite common for many 

 of the ordinary soil organisms tested. 



Adequate drying of hay and of grain prior to storage is of 

 paramount importance in the prevention of harmful and dangerous 

 self-heating. Microbial thermo gene sis also has some practical 



