XII.] FERMENTATIONS IN THE DUNG-HEAP 231 



urea and soluble carbohydrates in the straw, will get up 

 heat quickly and serve as material for a good hotbed. 

 A gardener is also accustomed to let manure in this 

 way get hot and turn it repeatedly before using it for 

 such purposes as the growing of mushrooms. Such a 

 process the gardener calls " taking the fire out " of the 

 manure, whereby he means that he has got rid of, in 

 fact burnt up, the easily fermentable material, and at 

 the same time he has reduced the amount of ammonia, 

 which otherwise might easily have become injurious to 

 the roots of tender plants. The fermentation of urea is 

 not, however, the only change in the nitrogenous 

 compounds that takes place. The undigested proteins 

 in the faeces and similar bodies contained in the litter 

 are attacked by the putrefactive bacteria; they are 

 resolved into simpler substances, and may eventually 

 break down as far as ammonia. At the same time, 

 however, certain reverse changes take place ; the 

 bacteria which develop in the dung are so enormous in 

 number that they take for themselves an appreciable 

 percentage of the soluble compounds of nitrogen there 

 present and convert them into insoluble proteins 

 forming part of their own tissue. The various changes, 

 which we have thus indicated as taking place during 

 the making of farmyard manure while it is still under 

 the feet of the animals, are also continued during the 

 storage process. After the manure has been made up 

 into a mixen or dung-heap, the changes become much 

 slower, and the loss of nitrogen is comparatively small if 

 the heap is kept moist and tightly packed. Losses of 

 nitrogen, however, are constantly occurring, and under 

 ordinary working conditions we must expect that only 

 about half of the nitrogen originally contained in the 

 food finds its way back to the land in the farmyard 

 manure ; of the other half some will have been retained 



