UIK 



ISO 







said to be irrigation, inasmuch as the 

 principal object is to kill weeds. 



The Dutch and Germans often dis- 

 tribute fluid manures by a system of 

 irrigated work. "Where a head of 

 water is wanting, pumps may be used 

 to raise it, the fluid running in a gut- 

 ter to the upper ditch. 



O 



Fig. 5. 



Fig. 5 is a simple kind of sluice to regulate 

 the flow of water. 



IRRITABILITY OF PL.\NTS. 

 Many plants, as the sensitive mimo- 

 sas, e.xhibit a power of contracting 

 their leaflets upon touch ; this phe- 

 nomenon, the most prominent of 

 those attributed to the irritability of 

 plants, is a mechanical function de- 

 pending upon the action of light. 

 443 



Plants possess no nervous system, 

 and are therefore incapable of volun- 

 tary motion, or any other than chem- 

 ical and mechanical movements. 



IRRITATION. In farriery, an in- 

 creased vascularity of any part, with 

 pain, but not amounting to inflamma- 

 tion. It is treated like inflammation, 

 but by milder means. 



ISCHIUM. The lower portion ot 

 the haunch bone. 



ISCHURIA. Retention of urine. 



ISINGLASS. Pure gdalin obtain- 

 ed from the sounds of fish ; it is also 

 manufactured from calves' feet, &c. 



ISNARDIA. A genus of aquatic 

 weeds. 



ISOLATED. In electricity, sur- 

 rounded by non-conductors, as glass, 

 dry silk, resin. 



ISOMERISM, ISOMERIC (from 

 <(TOf, equal, and fiepoc, part). Com- 

 pounds having the same number of 

 atoms of the same bodies, but exhib- 

 iting dissimilar properties, are called 

 Isomeric. Chemists consider that the 

 difference arises from a distinct group- 

 ing or aggregation of the atoms. 

 Very many organic bodies are isom- 

 eric, as starch {amylm) and dextiine: 

 On Hio Oio : cyanic and fulminic acids, 



