12 



Farmyard Manure. 



[APRIL, 



as the bacteria themselves multiply they seize upon the active 

 soluble forms of nitrogen and convert them into insoluble 

 proteins in their body tissues. Which action is predominant 

 will depend on the stage that has been reached in the dung- 

 making process, i.e., on the supply of carbohydrate, air, water, 

 and other variable factors, but after the first rapid production 

 of ammonium compounds the longer the dung is stored the 

 more the ammonia returns to a protein form. 



So far we have been considering only changes in the nitro- 

 genous material of the excreta and the litter, since nitrogen 

 is the chief fertilising constituent of the manure, but the 

 most characteristic change in dung-making is the destruction 

 of the straw and its conversion into dark brown " humus," 

 which in the end retains none of the structure of the original 

 straw. There are a number of organisms to be found commonly 

 in the air and dust which readily attack such carbohydrate 

 material as straw affords, and in the presence of oxygen burn it 

 up completely into carbon dioxide, water, and inorganic ash. 

 Such organisms, however, do not play a very large part in 

 manure-making, because air soon gets excluded from the 

 mass, and the work is taken up instead by other bacteria capable 

 of acting in the absence of oxygen. Two of these only have 

 been as yet studied with any detail ; they both rapidly attack 

 carbohydrates like cellulose and give rise to carbon dioxide, 

 marsh gas or hydrogen respectively, certain fatty acids of 

 which butyric is the chief, and the indefinite brown acid sub- 

 stance known as " humus," which is richer in carbon than the 

 original carbohydrate. 



A considerable proportion, amounting to one-quarter or 

 more, of the dry matter of the original dung is lost during this 

 process of humification, by the conversion of carbohydrates 

 into carbon dioxide, marsh gas or hydrogen, and water. The 

 various acids which are also produced are neutralised by 

 the liquid part of the manure, which is alkaline from the 

 presence of ammonium and potassium carbonates, resulting 

 from the fermentation of the nitrogenous constituents and 

 salts of the urine ; the dark brown liquid to be seen draining 

 from a dunghill is a solution of the humus formed in this alkaline 

 liquid. 



The changes going on during the making and storage of 



