CHAPTER XVI. 



THERMOGENIC BACTERIA. 



103. Spontaneous Combustion. 



THE state of our knowledge on the thermic side of the process of fermentation 

 does not extend beyond a few crude, isolated determinations, so that nearly 

 everything in this department has still to be accomplished; even the primary 

 question whether there exist; fermentative organisms with purely exothermic 

 and others with purely endothermic cell-activity being as yet unsolved. One 

 thing only has been established for certain, viz., that many microbes under 

 certain conditions generate heat and give it off to the environment. Hence the 

 chemical changes then occurring are exothermic processes. 



An example of this is affor led by the organisms effecting the so-called 

 spontaneous heating of hay and cotton. For sundry researches hereon we are 

 indebted to F. COHN (VIII.), from which it appears that fission fungi, allied to 

 the hay bacillus already several times referred to, are here concerned. That the 

 heating is actually the result of microbial activity was proved by Haepke, who 

 ascertained that sterilised cotton-waste, under otherwise identical conditions, 

 only became heated when moistened with washing-water from fresh unsterilised 

 waste. The heating only occurs in presence of oxygen, and comes tQ a standstill 

 when this substance is lacking, the action being the result of brisk oxidising 

 activity (respiration) on the part of the bacteria in question. The fluffy greasy 

 waste material formed during the cleaning and spinning of raw cotton, consisting 

 of cotton fibres, seed capsules, &c., spontaneously rises in temperature up to 

 67 0., according to the observations of Haepke, and becomes gradually con- 

 verted into a humous mass with evolution of the vapours of trimethylamine. 

 This observer attributes the fermentation occurring in this case to various 

 species of micrococcus. 



The heating of vegetable matter to high temperatures should not, however, 

 always be ascribed to the action of fissiun fungi. For example, the temperature in 

 badly managed heaps of germinating (malting) barley may rise to 60 C. and over, 

 the cause of which, according to the researches of COHN (IX. and X.), is a mould, 

 viz., the Asp'rgillus fumigatus, nearly allied to the common mould fungus. 

 That the diastase in the germinating barley is thereby greatly injured is cert dn. 



In many instances the spontaneous heating of the aforesaid vegetable 

 matters may develop into spontaneous combustion, whereby barns and spinning 

 works have often been set on fire. Nothing definite is known of the precise 

 conditions concerned in this phenomenon. In the first place, a knowledge of the 

 igniting temperature of the various substances under consideration is necessary, 

 and as this temperature is probably higher than the maximum heat supportable 

 by living organisms, the actual ignition in such cases cannot be directly attributed 

 to their vital activity. Hence, the probable explanation of spontaneous ignition 

 is that certain micro-organisms, by their oxidising action, convert the vegetable 

 fibres into a humous porous mass, which is then (like finely divided iron, &c.) 

 capable of occluding oxygen, whereby ignition is induced. More detailed researches 

 into this phenomenon are still required. 



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