i8o 



FARMYARD MANURE 



[chap 



to go through before they can reach the plant, and 

 having already shown themselves able to resist the 

 attack of the animal's digestive ferments they are 

 correspondingly unaffected by the ordinary decay 

 processes in the soil. The proportion the digestible 

 bear to the indigestible constituents of a food varies 

 with the nature and even with the mechanical condition 

 of the material, also with the kind and age of the 

 animal ; roughly speaking, the richer the food the 

 greaterthe proportion that is digestible — ^.^..decorticated 

 cotton cake contains 7 per cent, of nitrogen, of which 

 Zy per cent, is digestible and finds its way into the 

 urine, while hay contains about i'5 per cent, of nitrogen, 

 of which only 50 to 60 per cent, is digestible. 



When the animal consuming the food is growing or 

 fattening or yielding milk, a certain proportion of the 

 manurial constituents in the food is retained, the 

 proportion varying with the nature both of the food 

 and the animal. Cows in milk and young growing 

 animals take the greatest toll from their foods, animals 

 in the later stages of fattening the least. If, for 

 example, 100 lb. of linseed cake be fed to milch cows 

 and oxen nearly fat respectively, the manurial con- 

 stituents contained in the cake will be distributed in 

 each case as shown in Table XLIX. 



Table XLIX.— Nitrogen Retained and Digested. 



