IRR 



ISE 



tion and short rest. 6. All stimuli pro- 

 duce action in proportion to their 

 irritating powers. Ajs a person approaches 

 his hand to the fire, the action of all the 

 vessels in the skin is increased, and it 

 glows with heat ; if the hand be approach- 

 ed still nearer, the action is increased to 

 such an unusual degree as to occasion 

 redness and pain ; and if it be continued 

 too long 1 , real inflammation takes place ; 

 but if this heat be continued, the part at 

 least loses its irritability, and a sphacelus 

 or gangrene ensues. 7. The action of 

 every stimulus is in an inverse ratio to the 

 frequency of its application. A small 

 quantity of spirits taken into the stomach, 

 increases the action of its muscular coat, 

 and also of its various vessels, so that di- 

 gestion is thereby facilitated. If the same 

 quantity, however, be taken frequently, 

 it loses its effect. In order to produce 

 the same effect as at first, a larger quan- 

 tity is necessary; and hence the origin 

 of dram-drinking. 8. The more the irri- 

 tability of a part is accumulated, the 

 more that part is disposed to be acted 

 upon. It is on this account that the ac- 

 tivity of all animals, while in perfect 

 health, is much livelier in the morning 

 than at any other time of the day ; for 

 during the night the irritability of the 

 whole frame, and especially that of the 

 muscles destined for labour, viz. the mus- 

 cles of voluntary action, is re-accumulated. 

 The same law explains why digestion 

 goes on more rapidly the first hour after 

 food is swallowed than at any other time ; 

 and it also accounts for the great danger 

 that accrues to a famished person upon 

 first taking in food. 9. If the stimuli 

 which keep up the action of any irritable 

 body be withdrawn tor too great a length 

 of time, that process on which the forma- 

 tion of the principle depends is gradually 

 diminished, and at last entirely destroy- 

 ed. When the irritability of the system is 

 too quickly exhausted by heat, as is the 

 case in certain warm climates, the appli- 

 cation of cold invigorates the frame, be- 

 cause cold is a mere diminution of the 

 overplus of that stimulus which was caus- 

 ing the rapid consumption of the princi- 

 ple. Under such, or similar circumstances, 

 therefore, cold is a tonic remedy ; but if 

 in a climate naturally cold, a person were 

 to go into a cold bath, and not soon re- 

 turn into a warmer atmosphere, it would 

 destroy life just in the same manner as 

 many poor people, who have no comforta- 

 ble dwellings, are often destroyed from 

 being too long exposed to the cold in 

 winter. Upon the first application of 

 cold the irritability is accumulated, and 

 the vascular system therefore is disposed 



to great action ; but after a certain time 

 all action is so much diminished, that the 

 process, whatever it be, on which the 

 formation of the irritable principle de- 

 pends, is entirely lost. See Dr. Crichton 

 on Mental Derangement for more on this 

 subject 



ISATIS, in botany, a genus of the Te- 

 tradynamia Siliculosa class and order. 

 Natural order of Siliquosae or Cruciformes 

 Cruciferae, Jussieu. Essential character ; 

 silicle lanceolate, one-celled, one-seeded, 

 deciduous, bivalve ; valves nivicular. 

 There are five species, of which I. tincto- 

 ria, dyer's woad, is a biennial plant, 

 with a fusiform, fibrous root; stem up- 

 right, round and smooth, woody at 

 bottom, branched at top ; stem leaves 

 from two to three inches long, and scarce- 

 ly half an inch in breadth ; flowers 

 small, terminating the stem and branches 

 in a close raceme; both corolla and 

 calyx yellow ; petals notched at the end ; 

 seed vessels on slender peduncles, hang- 

 ing down, chesnut coloured or dark 

 brown, shining when ripe, of an oblong 

 elliptic form, compressed at top and on 

 the sides into a sharp edge, swelling like 

 a convex lens in the middle ; cotyledons 

 ovate, fleshy, piano convex ; radicle sub- 

 cylindrical, bent in upwards. It is a na- 

 tive of most parts of Europe. Woad is 

 much used by dyers for its blue colour : 

 it is the basis of black and many other 

 colours. 



ISCHJEMUM, in botany, a genus of the 

 Polygamia Monoecia class and order. 

 Natural order of Gramina, or Grasses. 

 Gramineae, Jussieu. Essential character : 

 hermaphrodite calyx ; glume two-flower- 

 ed ; corolla two-valved ; stamens three ; 

 styles three ; seed one: male, calyx and 

 corolla as in the other ; stamens three. 

 There are eight species. 



ISERINE, in mineralogy, a species ot 

 the Menachine genus : it is of an iron- 

 black, inclining a little to the brownish- 

 black ; it occurs in small, obtuse, angular 

 grains, and in rolled pieces, with a rough 

 glimmering surface. Internally it is glis- 

 tering, and its lustre is semi-metallic, 

 Specific gravity 4.5. Before the blow- 

 pipe, it melts into a blackish-brown 

 coloured glass, which is slightly attracted 

 by the magnet. It is composed of 

 Oxide of menachine . . 59.1 



iron 30.1 



uran. .... 10.2 



Loss. . . . 



99.4 

 6 



100.0 



