MANUAL OF AGKICULTUPtE. 251 



to the exact source whence the lymphatics directly absorb their 

 contents. They are supjDOsed to absorb the excess of liquor 

 sanguinis effused for nutritive purposes by the delicate capil- 

 laries into the tissues, and also such compounds resulting from 

 tissue changes as are not totally excrementitious, but capable of 

 further utilisation and absorption, after they may have been 

 more highly organised and again carried into nutritive circulation, 

 The nutritive substances being almost entirely absorbed by A'es- 

 sels leading into the veins, they are conveyed through several 

 organs, which elaborate them into various compounds capable of 

 being assimilated by the tissues before reaching the systemic 

 circulation. The excrementitious compounds formed by tissue 

 waste are absorbed by the blood-vessels, and these vessels lead- 

 ing into other organs capable of extracting all deleterious matter 

 from the blood, the circulating fluid leaves them freed from 

 waste and noxious compounds before it again permeates the 

 different parts of the system. In further organising the absorbed 

 nutritious compounds, the liver takes an important part, as also 

 do the glands of the lacteals and lymphatics and the lungs as 

 well. The principal agents in removing superfluous matter from 

 the blood are the kidneys, lungs, liver, and skin. The kidneys 

 secrete from the blood the excess of moisture, the waste albumin- 

 ous substances, and nearly all the mineral salts in solution, all 

 of which are conveyed from them to the bladder, and thence 

 voided as urine. In the lungs the venous blood gets exposed to 

 the oxvt^en there inhaled in the common air, and such blood 

 greedily absorbs the oxygen. Carbon and hydrogen combine 

 with it, and are exhaled with the expired breath as carbonic 

 acid and watery vapour. The oxygen combines with the blood's 

 colouring matter as well, and is readily yielded up by the latter 

 to the tissues, in order that there may be effected the oxidisation 

 and chemical change of their component substances. Besides 

 its functions in the process of digestion and of organising com- 

 pounds absorbed by the blood, the liver has to discharge the 

 supplementary one as well of purifying the blood from the 

 2)resence of certain bodies, which are for the most part com- 

 pounds of carbon and hydrogen. The skin excretes gases and 

 moisture — carbonic acid and watery vapour for the most part ; 

 but also minute quantities of compounds similar to those in 

 urine, and tliis in the acts of sensible and insensible perspiration 

 alike. Such compounds as those last njentioned are also to some 

 extent exhaled from the Jungs. 



Tile i)riiicii)al bodily excretions are urine and the fivces, whicli, 

 committed to the soil, are still of value for the purposes of plant 

 life. Urine, as we liave seen, chiefly contains disorganised alhu- 

 miiious compounds and inorganic salts. Sunnnarily, the different 

 compounds of fieces may be stated to be those winch have been 



