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IRR scum will be generated, vrhich is very pernicious to the grass; and, if the water be drawn off, and the land exposed to a severe frosty nighty without being previously dried for a whole day, the greater part of the tender plants will be to- tally destroyed. In the beginning of March, the grass on well-flooded meadows will, in general/ be so forward as to fur- nish abundant pasturage 3 when the water should be drained for the space of a week, that the soil may become firm, before heavy cattle be allowed to graze on such land : these, however, if the season be cold, ought to be supplied with a little hay every night, during the first week. In the month of April, the grass may be eaten down closely ; but no cattle should be turned in later; as otherwise the crop of hay will be much impaired ; the grass be- come soft or woolly ; and conse- quently its value be considerably diminished. In the beginning of May, the water is again thrown over the soil for a few days, in order to moisten it ; but the pradtice ought on no account to be continued during the summer; for it has an unfavourable effeft on the after-viath ; and pro- duces in sheep fed on it^ the dis- order called the rot. Many other advantage* arise from irrigation ; but, as our limits admit only of giving an outline, we refer those readers who are de- sirous to acquire farther informa- tion relative to this interesting branch of rural economy, to Mr. G. Boswfxl's Trealhe on JP'aUr- hig Meadows, &c. (8vo. 2s. 6"d. l/SO), in which the necessar)- im- plements, and terms employed in irrigation/ are explained and illus- IRR trated wllh engravings ; as like- wise to Mr. Wright's Art of Floa' big Land, Sec. (2d edit. 8vo, Hatchard, I7P9, pp. go, 3s. 6d.) j where the subject is perspicuously treated, and objedions are abljr answered. IRRITABILITY, denotes that essential property of animals, in consequence of which their fibres, on being touched, contra£l or be- come short, in a greater or less degree. Chemists have lately endeavour- ed to shew, that all animal and vegetable irritability originates from die oxygen, which is inhaled by the lungs, or respired by the leaves, or absorbed by the roots. And as re- spiration is every minute requisite to the support of animal life. Dr. Darwin conjeftures that some- thing immediately necessary to their existence, is acquired by the lungs of animals from the atmosphere, ri>ther than from the food they di- gest ; and that this nameless some- thing, perhaps oxvgen, is mixed with the blood, and again separated from it by the spinal marrow, after having undergone certain changes in the course of its circulation, or secretion. In a similar manner, he considers it as probable that the spirit of vegetation may be derived fiom that source, namely, the un- combined oxygen of the air, which is respired by the upper surfaces of the leaves, and not from that which is absorbed b}' roots, in a more combined state : farther, that thW oxygen is again separated from the juices bv the sensDrium, or brain, of each individual bud, after having undergone some change in its pas- sage through the secretory vessels, A long-continued, unusual, or unnatural stimulation of vegetable fibres/ by an iucrcase oi'.heat, e'x- ' hausts
