XII.] MANURIAL VALUE OF EXCRETA 227 



digested gets excreted in a liquid and soluble form, and 

 is therefore in an available state for the plant, whereas 

 the same constituents in the faeces are insoluble, and 

 only reach the plant after the lapse of some considerable 

 time. We have also learnt in the previous chapter that 

 the richer and more concentrated a food is, the greater 

 is the proportion of its nitrogen that is digested. For 

 example, decorticated cotton cake contains nearly 7 per 

 cent, of nitrogen, and about nine-tenths of that nitrogen 

 is digested and reappears in the soluble active form of 

 urea; whereas hay only contains about i^- per cent, of 

 nitrogen, of which barely half is digestible, while the 

 other half is excreted in a solid form and will form but 

 a slow-acting fertiliser. Thus an animal which is fed 

 with concentrated cakes and meals, such as a bullock 

 during the fattening process, will be giving rise to much 

 richer manure than animals which are being kept in a 

 store condition and only receiving such low-grade foods 

 as hay, straw, and roots, even though the same amount 

 of nitrogen is being consumed in the two cases. We 

 have thus a number of factors affecting the composition 

 of farmyard manure. Young growing stock take 

 nitrogen from the food in order to make flesh, and 

 phosphoric acid in order to make bone ; milch cows take 

 both phosphoric acid and nitrogen for their milk ; store 

 stock and working horses do not receive very concen- 

 trated food, and in their turn give rise to comparatively 

 poor manure. The animals themselves induce a certain 

 amount of difference, and though the composition of the 

 excreta varies so much with the age and food that 

 analyses are not of much information unless large 

 numbers are given, it will be found that the urine of 

 sheep and horses is more concentrated than that of 

 cattle and pigs, and similarly, that the solid excreta 

 of the two former are also drier. It is this greater 



