130 THERMOGENIC BACTERIA 



removal of the water, of which the plants now under consideration contain some 

 85 per cent., can be effected in two different ways. Either the necessary heat 

 is applied from outside, i.e. they are exposed to the sun's rays, thus producing 

 air-dried hay, or else the same result is obtained by spontaneous heating, and 

 therefore by the action of the thermogenic micro-organisms dwelling on the 

 plants. Here again there are two possible methods of procedure, by following 

 one of which burnt hay is obtained. On this subject we are indebted to 

 BOHMER (I.) for a critical research. According to him, the mown grass is piled 

 up into heaps about 10 to 13 feet high and 13 to 16 feet in diameter, the mass 

 being trodden down as tightly as possible in order to prevent the admission 

 of air which might favour the development of mould into the interior. In 

 these heaps spontaneous heating goes on and becomes apparent, often within 

 twelve hours, but generally in twenty-four to thirty hours. The operation is 

 watched, and as soon as the temperature inside the heap reaches 70 C. which 

 is mostly the case in forty-eight to sixty hours the heaps are opened and the 

 contents spread out thinly, a single turning being then sufficient to complete the 

 curing of the hay. By this fermentation, about which nothing definite is known 

 from the physiological point of view, not only is the desired degree of dryness 

 attained, but the hay also becomes friable and acquires an aromatic odour. 



As mentioned above, the heaps must be opened when the temperature has 

 risen to 70 C., since, if this be neglected, the spontaneous heating will quickly 

 become spontaneous ignition. If, as is possible, it is rainy when the hay is 

 ready for spreading out, such preliminary labour is futile. To this circum- 

 stance is due the fact that burnt hay is seldom prepared, as also that, in 

 districts where the weather is too uncertain to allow of ordinary haymaking 

 being conveniently practised, another method of drying has been developed, in 

 which the necessary heat is likewise generated by a process of fermentation, from 

 which a product known as " brown hay " is obtained. This will be dealt with in 

 the Section on Lactic Fermentation. 



