PUR
Of the ramofe, or branched purpura, with fhort tails, we have the following fpecies preferred in cabinets. I. The rough purpura, with a flefh-coloured lip, armed with three rows of branches. 2. The yellow purpura, with three rows of high branches. 3, The tribulus, or whitifh purpura, with three rows of lefs jagged branches. 4- The fine armed purpura, with the branches^jagged in the manner of the foot of a toad, with a diftinct clavicle. 5* The lefs rough purpura, with fix rows of branches. 6. The curled lettuce purpura, jagged from the head to the bafe, and having fix rows of branches. Of the fpinofc purpura with long tails, we have thefe : 1. The great fpinofe purpura, with very long fpines. 2. The fmall fpinofe purpura, with three rows of Shorter fpines. 3. The fmaf! rough purpura.
Of the purpura covered with tubera, having a long beak and long tail, we have the following : 1. The woodcock purpura, with a long tail and no fpines. 2. The lefs fpotted woodcock purpwa. ?. The fmali brown woodcock purpura. Of the thick collated, or ribbed purpura, with crooked beaks, we have the following fpecies: 1. The marble collated and tuberous purpura, with blue fafcise. 2. The fpinofe marbled purpura.
Of the hairy purpura, with long clavicles, we have the fol- lowing fpecies: j. The grey purpura, with three rows of fpin s or hairs, with an erected clavicle and ftrait beak. 2. The crooked beaked hairy purpura, with feveral fe.ofe fim- briae.
Of the thin oculated purpura, with compreffed clavicles and fhort beaks, we have the following fpecies : 1. 1 he fea-por- cupine, or oculated purpura. 2. The porphyry purpura. Hift. Nat. Eclairc. p. 298.
The purpura is a fhell-nfh very well known, and has been known alfo in almoft all times to afford a purple liquor; but as there has been no method difcovered of bringing this liquor into ufe in dying, the fiih has been negle£ted, and its juice never attempted to be brought into ufe.
The juice which gives this beautiful purple colour is, while it remains in the body of the animal, and while that is in health, wholly white ; but no fooner is it expofed to the fun, than it begins to change colour, and in lefs than five minutes goes through the feveral changes of pale green, yellowiib, and a beautiful emerald green : nfter this it becomes of a deeper and dufkier green, then bluiih, reddifn, and finally a deep and very beautiful purple. Sometimes the juice is found naturally green in the animal ; this is probably from the creature's be- ing in a difeafed ftate : but when it is naturally thus, it im- mediately becomes red, and afterwards purple, on being ex- pofed to the fun, its feveral preceding changes feeming to have been made already in the body of the animal. If a piece of linnen be rubbed over with this juice, and part of it expofed to the fun, part not, that only will turn red which is fo expofed, the other remaining green without any alteration ; and it is obferved,' that the ftronger the fun mines, the quicker the change appears, and probably the colour is in proportion alfo the more beautiful and lively. And it is very remarkable, that if a needle, or any other opake body, be laid upon the linnen which is yet green, and is to become red on being expofed to the fun; after fuch an expofure the whole fnall be changed red or purple, excepting only that fmall fpot which is covered by th^ needle, which will ftill remain green.
A plate of glafs, tho' it be three inches thick, will not prevent the colour from changing purple by being laid over it; but the thinned piece of metal will keep it wholly green. The one being opake, and the other pellucid, are evidently the only rcafons for this difference.
If the coloured linnen be fucceffively covered by three pieces of paper, the one blacked with ink, the other in its natural irate, and the third rubbed over with oil, it will change co- lour on being expofed to the-fun in different degrees ; and that exactly in proportion to the degree of tranfparence in each of the papers : moft of all in that which was covered with the oiled paper, Something lefs than that covered by the paper in its natural ftate, and leafr. of all in that which was covered with the blacked paper, as that is Ieaft transparent. The common heat of a fire, or that of a red hot iron, pro- duce no change at all in the colour when green. The vapour of burning Sulphur produces a little; but the green which had not changed to purple by thefe experiments, immediately changed to it on being expofed to the rays of the fun. Thefe experiments were all made in the months of January and February, by Mr. Du Hamel, in Provence; and the fun having power to change the colour fo fpeedily there in thefe cold months, probably in a warmer climate or feafon the air would have been fufneient for the purpofe, without the open fun ; fince it feems, from experiment, that both the folar rays, and the light alone in a cloudy day, can a£t upon this colour. The light and heat of the fun both a£t on this colour: light is always fufneient to produce the effect; but the heat may eafdy be too great, or too little, and to do the whole in per- fection it muff be at a certain middle degree. This beautiful, purple, if it can ever be brought into ufe in dying, will have one very great advantage from its vifcofity The pieces of cloth that had been Stained by it retained their
PUR
colour, in Spite of feveral boilings in different Kqtiorf, which Mr. Du Hamel made them pafs through ; and the colour, on examination, was found not to be fuperficial, but penetrated the whole body of the fluff which was tinged by it. There are many inconveniences which muff naturally attend the ufe of this fubftance as a dye, but they may, perhaps, all be <*ct over by care and application. It is very certain* that it is of too vifcid a nature eafily to penetrate many fubftances j but it is alfo certain, that this might be obviated by difiblving it in fome proper liquor. It appears very plainly, that the antients had a method of thu3 difiblving their purple ; but we neither know what was their purple, nor what was its duTolvent; nor, which would be of much more confequence to us at prefent, what is the proper difiblvetit for our own. Mem. Acad. Scien. Par. 1730.
Pcrjian Purpura, the fame v/ith the PerSian-fhell, a fpecies of dolium. See Dolium.
PURPUREA febtis, the purple fever, in medicine, the name gi- ven by authors to a fpecies of fever, called alfo by fjme a mi- liary fever.
It is an acute, continual, and exanthematous/kw, in which nature feems to be endeavouring to drive out the fubtle mor- bific matter to the furface of the body, by increasing her fe- cretory and excretory motions, funhr's Confp. Med. p. 325. This fever is divided into two kinds; of the which, one is called purpura rubra, or the red purple fever ; and the other by a very odd form of expreSIion, the purpura alba, or white purple fever.
The white purple fever is ufually malignant; it is eafily com- plicated with the petechial fevers, and in fome places has of* late years been found often to affect lying-in women. The red purpura is much more benign and mild than this, and, indeed, often is attended with no danger. Thefe two fpecies of purpura feem to differ as much as the fmall-pox and meailes do from one another, the white /kw of this kind being ufually as much more fatal than the red, as the fmall-pox is mere fatal than the meafles ; but as there are cafes in which the fmall-pox is mild and benign, and the meafles are Sometimes dangerous, fo in thefe difeafes, out of the na- tural courfe, the white is fometimes mild, and attended but with a flight fever, while the red is fatal, and attended with a very high one. As the fmall-pox alfo has white puftules, and the meafles only protuberances on the fkin ; fo the white purple fever has alfo regular white puftules, while the red has only fuch protuberances as thofe of the mealies. f..nk\ Confp. Med. p. 327.
Signs of thefe difeafes. The white kind feizes the patient with a general fhivering and coldnefs, and a ftraitnefs of the pras- cordia, with great anxiety of mind, and afterwards fhews it- felf in alternate changes of heat and cold ; and before the ap- pearance of the eruptions, the patients are worfe in refpect of their anxiety and other fymptoms, and complain of a trouble- fome itching under the fkin. The puftules ufually iirft appear on the fourth day, fometimes later; and at their approach, there is firft perceived a general redhefs of the fkin, and after this the rednefs is collected into fpots, in the middle of each of which there appears a white puilule ; and thefe are often fo copioufly fpread over the body, that they almofl: touch one another. Thefe puftules are pellucid, and contain only a clear water, and their eruption is ufually attended with an acute fever; when thefe puftules have flood four days, they dry away, and the places appear fcaly, and the difeafe termi- nates. Sometimes in people of humid habits, and fuch as have no fever, thefe puftules fweat out a white water. The red purple fever feizes the patient in nearly the fame way with the white, that is, with Shiverings and heat fuc- ceeding one another. It is alfo attended with a tenfion and pain in the back, and with a ftraitnefs of the breaft and a cough. The purple eruptions appear on the fourth, or on the feventh day, or later even than that, in form of fmall protube- rances, like millet-feeds ; and are attended at the time of their eruption, with an itching within the fkin: the fever is not violent, and the fweat is copious, and of an ill fmell. In fome cafes this difeafe is attended with no fever at all, and' people go about their bufinefs with it, only complaining of an itching all over them. Some have violent pains of the head at the time, and are fleepy and anxious they know not why ; but thefe fymptoms ufually go off as foon as the eruptions ap- pear properly : thefe remain fully out a few days, and then die away of themfelves, and the perfon finds himfelf as well as before.
The purple fever of both kinds feems to have been more fre- quent of late than in the times of the earlier writers on medi- cine. The white kind in particular, fome years ago, was in a manner epidemic in Saxony, and carried off great numbers, and particularly feized the lying-in women. Wherever the petechial fevers are frequent, there the white purple fever is ufually alfo common. It often alfo mixes itfelf with the fmall pox, and makes the cafe always greatly worfe, and all the fymptoms more violent. TKe-red purple fever is mod frequent with young men, and fuch as lead fedentary lives, and are fubjeft to violent paffions ; labouring people are fcarce ever found affected with this difeafe Among worsen, thofe of tenderer confiitutions are moft Subject to it,' and especially fuch
