10 PEECENTAGE OF FOOD IN EXCRETA. 



again indebted to Wolff's investigations for valuable 

 information on this point. He has found that the 

 following percentages of organic matter, nitrogen, and 

 mineral substances, originally present in the dry matter 

 of the food, are voided in the urine : 



We have now considered briefly the composition 

 of the solid excrements and urine of the common 

 farm animals, and have also enumerated some of 

 the principal causes of the variation in their compo- 

 sition. 



The solid excreta consist, as we have seen, of 'un- 

 digested food, while the urine contains the manurial 

 ingredients of the food which have been digested by 

 the animal system. 1 The latter is, weight for weight, 

 as a rule, very much more valuable as a manure than 

 the former. From the table given in the Appendix 2 

 it will be seen that the proportions of the nitrogen 

 and ash constituents, originally present in the food 

 consumed, which are voided in the excrements, vary 

 with different circumstances. Wolff, in summarising 

 his results, points out that, as a rule, the solid and 

 liquid excrements will contain about 46 per cent of 



1 The nitrogen present in the urine, it may be well to point out, 

 is derived from the waste of nitrogenous tissue as well as from nitro- 

 genous matter of the food digested. 



2 Note IV., p. 55. 



