From these figures we see that, in their natural condition, the excreta of the sheep are the most valuable; those of the horse and pig coming next; while those of the cow are the poorest, containing one-third as much nitrogen as those of the sheep, and one-half as much as those of the horse and pig. This difference, however, is due almost entirely to the different percentage of water the excreta of the various animals contain in their natural state; for in the dry state they are seen to contain, with the single exception of the pig, practically the same amount. In conclusion, then, the important points to be noticed are-- 1. That in the passage of the food through the system of the common farm animals, only a very small percentage of the fertilising substances, nitrogen, phosphoric acid, and potash, is assimilated and retained in the animal body; and that, therefore, theoretically at least, the excreta should contain nearly the same amount of fertilising matter as the food originally did. 2. That even in the case of a fattening animal, the loss of fertilising matter sustained by the food in passing through the system is not great. 3. That with regard to the total amount of solid excreta and urine voided, the latter contains, as a rule, more nitrogen than the former; the nitrogen in the urine, further, being more valuable, as it is in a soluble condition. 4. That as regards the distribution of the ash-constituents, _lime_, _phosphoric acid_, and _magnesia_ are almost entirely found in the solid excrements; while the urine contains nearly all the _potash_. 5. That the best results can be expected only when the liquid and solid excreta are used together as a manure. As the composition of the manure depends so largely on the nature of the food, a table will be found in the Appendix, Note VI.,[142] containing the manurial composition of some of the commoner feeding-stuffs. 3. _Litter._ We have now to consider the third constituent of farmyard manure--viz., the _litter_, which generally consists of straw. The uses of the litter, in addition to providing a dry and comfortable bed for the animal, may be briefly summed up as follows:-- 1. To absorb and retain the liquid portion of the excreta. 2. To increase the quantity of the manure, and thus secure its more equal distribution when applied to the field than could otherwise be done. 3. To add to its value as a manure, both physically and chemically. 4. To retard and regulate the decomposition of the excreta. Of course litter also performs a very useful function sanitarily, inasmuch as it serves to keep the stall or byre fresher and cleaner, and more free from noxious gases, which it absorbs, than would otherwise be the case.