770 JOURNAL OF FORESTRY 



might, under certain conditions, cause its bursting into flame. Due to 

 the efforts of Mitscherlich, Ellenberger, and others, the fact was estab- 

 lished that the fungus flora of the intestines of herbivorous animals 

 contains many forms of bacteria of the cellulose dissolving type. These 

 organisms, undei^ anaerobic conditions, break down cellulose into 

 methane, carbon dioxide, and water, the methane, of coiu'se, being an 

 inflammable gas. The question might arise as to whether anaerobic 

 conditions actually prevailed in this particular pile of dung, but it is 

 entirely possible, since, due to rapid drying, the outer surface was more 

 or less "case hardened" and due to the decomposition going on in the 

 interior of the heap, the oxygen was gradually used and no irore, or 

 very little more, entered, due to the continual internal gas pressure. 



It is a question if the heat release due to the above decomposition 

 would raise the temperature sufliciently high actually to cause the 

 material to ignite. Authorities differ as to whether or not the heating 

 of manure piles and of damp hay is a bacterial phenomenon. Some 

 writers on the subject hold that some cases of "spontaneous com- 

 bustion" should be attributed to the agency of the thermogenic bacteria 

 and that although the train of events leading to the actual bursting into 

 flame is not fully understood, bacteria play a part in the initial stages 

 of the process. Miehe, after an exhaustive investigation of the subject, 

 presents strong evidence of the thermogenic power of certain micro- 

 organisms. Still other writers in this field maintain that the heating 

 process is due to chemical reaction unaided by bacterial activity. Must 

 of the later observations tend to support the latter theory. 



In this particular case the shape of the droppings may also have been 

 a contributing factor. The individual parts of the dung heap being 

 more or less spherical in shape, may in some way have concentrated the 

 light in the same manner as a lense and the temperature thus raised to 

 the kindling point. Then, too, a spherical surface represents the mini- 

 mum surface area for any given volume and hence would be a minimum 

 amount of radiation. It is probable, then, that the above discussed 

 combustion was due to a combination of bacterial, chemical and physical 

 conditions, but it is not improbable that this same combination of 

 conditions may recur at any time and result in a forest fire. 



