PORDENONE POROSITY. 



643 



and appears to divide the tooth into two portions 

 there are also small lines of enamel radiating fron 

 the centre, which are worn down by attrition ; th 

 muzzle is thick and truncated ; the lip divided ; the 

 tongue furnished with spiny scales ; the ears shor 

 and rounded ; the anterior feet furnished with fou 

 toes, and the posterior with five, all armed will 

 thick nails. Cuvier divides this genus into hys 

 trix, at/ietura, eretison, and synethera ; the firs 

 including the common porcupine ; the second, th 

 fasciculated porcupine; the third, the Canadian 

 porcupine ; and the fourth, the porcupine with 

 prehensile tail. 



The common porcupine (H. cristata) is found in 

 the southern parts of Europe and in Barbary 

 When full grown, it measures nearly two feet in 

 length, and some of its spines exceed a foot. Its 

 general colour is a grizzled, dusky black. The 

 upper part of its head and neck is furnished with 

 long, light coloured hairs, capable of being raisec 

 or depressed at pleasure ; most parts of the back 

 and sides are armed with spines, which are longest 

 on the centre of the back. In their usual position 

 they lie nearly flat upon the body, with their points 

 directed backwards ; but when the animal is excited, 

 they are capable of being raised. The common 

 porcupine, though known from the earliest ages, 

 has given rise to numberless fables, among which 

 that most commonly received is, that it possesses 

 the power of ejecting its quills to a considerable 

 distance when irritated or pursued. The use oi 

 this armature does not appear to be well under- 

 stood ; the most probable supposition, however, is, 

 that, like that of the hedgehog, it is merely for 

 defence, as, like that animal, it has the power of 

 rolling itself up in a ball, and thus presenting a 

 phalanx of spears on every side, that renders the 

 attack of most animals fruitless. The porcupine 



generally sleeps during the day, and only leaves its 

 IUTOW in the evening, in search of its food, which 

 is almost entirely composed of vegetables. In cap- 

 tivity it is quiet and peaceable, but shows no marks 

 of attachment or familiarity. 



Canada porcupine (H. dorsata) is a very un- 

 sightly and sluggish animal, and is not provided 

 with the long quills so remarkable in the last-men- 

 tioned species, its armature consisting of short, 

 sharp spines, almost concealed by the hair with 

 which they are intermingled. It is about two feet 

 long, of a brownish colour mingled with white; 

 the spines are attached in a very slight manner to 

 the animal, and, from being barbed at tip with 

 numerous small reversed points or prickles, they, 

 by degrees, penetrate very deeply into the flesh 

 after having once pierced it. Small and insignifi 

 cant as these defensive weapons may appear, they 

 are capable of causing the death of dogs, wolves, 

 or indeed of any animal that incautiously attempts 

 to seize the porcupine. These spines or quills are 

 much used among the Indians to ornament different 

 articles of dress : they dye them of various colours, 

 in a very permanent manner. The Canada porcu- 

 pine is principally found in the northern parts of 

 the United States and in Canada. They feed on 

 the barks of various trees, apples, com, &c. Their 

 flesh is said to be very unpalatable, resembling 

 flabby pork. They pair about the latter end of 

 September, and the female brings forth two young 

 in April or May. 



PORDENONE (so called from his birth-place, 

 his true name being Giovanni Antonio Licinio), or 

 REGILLO DA PORDENONE, a painter of the Venetian 

 school, and rival of Titian, was born in 1584, and 

 executed many works for his native place ; some 

 also for Mantua, Vicenza, Genoa ; but his greatest 



works for Venice. For this city he painted the 

 chapel of St Roch, and the hall of the Pregadi, in 

 conjunction with Titian, with whom he also painted 

 in St John's church, whence a constant rivalry 

 existed between them. He died in Ferrara, whither 

 he had been invited by the duke Ercole II., to 

 prepare cartoons for Flemish tapestry (arazzi.) 

 His death was attributed to poison. He is distin- 

 guished for bold and lively colouring. 



POROSITY, an essential property of bodies, is 

 best ascertained by the microscope, which shows 

 us the passage of fluids through solid bodies; or 

 we may discover this property in the transmission 

 of light, in all directions, through the internal 

 structure of hard and solid bodies. The porosity 

 of wood is very remarkable. Air may be blown, 

 by the mouth, in a profuse stream, through a 

 cylinder two feet long of dried oak, beech, elm, or 

 birch and if a piece of wood, or a piece of marble, 

 be dipped in water, and submitted to experiment 

 under the receiver of a pneumatic machine, the air 

 issuing through the exterior cavities will appear in 

 a torrent of cubbies on the external surface. In 

 like manner mercury is forced through a piece of 

 dry wood, and made to fall in the form of a fine 

 divided shower. If a few ounces be tied in a bag 

 of sheep skin, it may be squeezed through the 

 leather by the pressure of the hand, in numerous 

 minute streamlets. This experiment illustrates 

 the porosity of the human cuticle. From micro- 

 scopic observations, it has been computed that the 

 skin is perforated by a thousand holes in the length 

 of an inch. If we estimate the whole surface of 

 the body of a middle-sized man to be sixteen square 

 feet, it must contain no fewer than 2,304,000 pores. 

 These pores are the mouths of so many excretory 

 vessels, which perform that important function in 

 the animal economy, insensible perspiration. The 

 lungs discharge, every minute, six grains, and the 

 surface of the skin from three to twenty grains, the 

 average over the whole body being fifteen grains 

 of lymph, consisting of water, with a very minute 

 admixture of salt, acetic acid, and a trace of iron. 

 If we suppose this perspirable matter to consist of 

 lobules only ten times smaller than the red par- 

 Jcles of blood, or about the 5000th part of an inch 

 n diameter, it would require a succession of 400 

 of them to issue from each orifice every second. 

 The permeability of a solid body to any fluid, 

 depends, however, on its peculiar structure and its 

 relation to the fluid. A compact substance will 

 sometimes oppose the entrance of thin fluid, while 

 t gives free passage to a gross one. Thus a cask, 

 vhich holds water, will permit oil to ooze through 

 t ; and a fresh, humid bladder, which is air-tight, 

 vill yet, when pressed under water, imbibe much 

 of that liquid. If a cylindrical piece of oak, ash, 

 :lm, or other hard wood, cut in the direction of its 

 bres, be cemented to the end of a long glass tube, 

 water will pass freely through it, in divided stream- 

 ets ; but a soft cork, inserted into a similar tube, 

 will effectually prevent all escape of the liquid, 

 tfercury may be carried in a small cambric bag, 

 which could not retain water for a moment. If a 

 ircular bottom of close-grained wood, divided by 

 a fine slit (from the 30th to the 100th part of an 

 nch wide), be cemented to the end of a glass tube, 

 t will support a column of mercury from one to 

 hree or more inches high, the elevation being 

 always proportional to the narrowness of the slit. 

 ience a cistern of box-wood is frequently used for 

 >ortable barometers, the fine joints admitting the 

 ccess and pressure of the air, but preventing the 

 scape of the mercury. Yet a sufficient force would 

 vercome this obstruction ; and, in the same 

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