308 SOILS AND MANUEES 



the manure is necessarily much richer than when the 

 animals are fed entirely on coarser and more bulky 

 fodders, such as hay, straw and roots. It will presently 

 be shown, however, that this is due mainly to the differ- 

 ence in the composition of the urine. 



The Urine. The solid constituents of the urine or 

 liquid excrement are derived directly or indirectly from 

 the digested portion of the food which is absorbed into 

 the blood and is used to form the tissues. Owing to 

 various physiological changes which take place, only a 

 comparatively small proportion of the nitrogen and ash 

 ingredients are permanently retained by the animal. 

 The amount varies according to circumstances, but by far 

 the largest part is ultimately discharged in the urine. 



In the case of horses and store animals, practically 

 the whole of the fertilising ingredients of the digested 

 portion of the food passes into the urine. Growing and 

 fattening animals retain a certain amount wherewith to 

 build up new tissues, and a still larger proportion is 

 utilised in the production of milk by cows and other 

 animals. Whatever is recovered in the shape of animal 

 produce, e.g., meat, milk, wool, etc., is lost to the manure. 



The relation between the food consumed and the pro- 

 portions of fertilising ingredients voided in the dung 

 and urine, and recovered in the shape of animal pro- 

 duce, is shown in the tables 1 on p. 309. 



It will be seen that, as a rule, from 60 to 80 per cent, 

 of the nitrogenous matter of the food is voided in the 

 urine, and from 20 to 30 per cent, in the dung. The 

 combined excreta contain from 75 to 95 per cent, of the 

 total nitrogen, and from 90 to 98 per cent, of the ash 

 ingredients of the food. Phosphoric acid enters into the 

 composition of animal tissues and a considerable pro- 



1 Warington ; " Chemistry of the Farm." 



