81T 



MOXA. 



MUDAR. 



813 



moment acting efficiently against the water : the value of v would be, 

 of course, determined by the number of revolutions which the wheel 

 makes in a given time ; and it should be expressed by the number of 

 feet per second which the centre of percussion in the paddle moves 

 through in turning about the axle. 



The momentum of water flowing horizontally against a plane, such 

 as a float-board of an undershot wheel, depends on its velocity, on the 

 area of the surface with which it comes in contact, and on the obliquity 

 of that surface to the direction of ita motion ; and in estimating the 

 effect of water on such a wheel, it is necessary to determine from the 

 dimensions of the channel and the velocity of the water in it the weight 

 of water which descends vertically through a certain height, as one 

 foot, in a given time. The product of this weight multiplied by the 

 height actually descended, being compared with the product of the 

 number of pounds which the wheel can raise to a certain height in 

 the same time multiplied by that height, expresses the ratio of the 

 ] nver to the effect. From many experiments, Mr. Smeaton concluded 

 th;it, when the quantity of water expended is the same, the useful 

 result varies nearly with the head of water, or with the square of its 

 velocity. 



The power of an overshot wheel is estimated by the product of the 

 weight of water expended in a given time multiplied by the whole 

 weight of its descent that is, by the sum of the diameter of the 

 wheel and the height of water in the reservoir above the top of the 

 \vhi.vl. The useful effect of an overshot wheel is said to be nearly 

 dnulile that of one which is undershot. 



In determining the power of water on breast-wheels, it is customary 

 to consider such a wheel as one compounded of an undershot and of an 

 overshot wheel ; and its effect is conceived to be equivalent to that of 

 an undershot wheel whose head of water is equal to the difference in 

 height between the surface of the water in the reservoir and the point 

 at which the water impinges on the wheel, together with the effect of 

 an overshot wheel whose height is equal to the difference between the 

 point of impact and the level of the tail-water. 



MOXA, a word of uncertain origin, signifying any substance whose 

 gradual combustion on or near the skin is used for the relief or cure of 

 I. This method was early practised in the East, particularly by 

 tin' < 'liinese and Japanese, from whom it was copied by the Portuguese ; 

 but having fallen into disuse, it was revived by the French surgeons 

 during the Egyptian campaign. The substance employed by the 

 Chinese ia formed of the downy covering of the leaves of the A rlemisia 

 Sfoxa (De Candolle) : but the down of many other plants, or the pith, 

 may be used. The stalk containing the pith of the common sun- 

 flower (Iltliaitthus annutu) is a very convenient means, when the 

 prepared moxas cannot be procured. Those used in Britain are all 

 imported from France, and generally consist either of a pyramidal or 

 cylindrical roll of linen, which is mostly steeped in a solution of nitrate 

 or chlorate of potass. The size of this is generally about eight lines 

 high, and from four to five broad. It is ignited at the one end, and 

 the combustion gradually extends to the other. This differs from the 

 actual cautery by means of a red-hot iron, inasmuch as the latter pro- 

 duces immediately its maximum of effect, which progressively dimi- 

 nishes, while in the case of the moxa the heat gradually increases, and 

 the greatest effect is produced towards the end of the operation. It is 

 also different from a blister, both in its mode of action and in the stage 

 of a disease in which it may be most advantageously applied. The 

 1 principles which should regulate the use of blisters having been 

 already explained [BLISTER], as well as those connected with the actual 

 cautery [EsCHAROTics], the following observations refer to the dis- 

 tinctive characteristics of the Moxa. We may remark that the pain is 

 not so great as might be expected, indeed less than often attends 

 blisters, and that it is often borne by females and children, or at 

 least boys, with the greatest fortitude. 



Besides the secondary effects of the local application, which, being of 

 a counter-irritative kind, are common to blisters and moxa, in the case 

 of the latter there is the additional influence of a certain amount of 

 caloric. "Caloric, applied under certain circumstances and with 

 appropriate restrictions, stimulates in a powerful manner the capillary 

 vessels, causing them to contract their diameters, and to circulate 

 their blood with greater velocity; and, either by this action on 

 the capillaries, or by a direct one on the lymphatics of the part, it 

 ha* also the power of exciting the function of the absorbents 

 in a'remarkable manner. -The direct effects of moxa are seldom, if 

 ever, confined to the skin ; and if the moxa be applied through the 

 medium of a needle, the caloric may be made to propagate its influence 

 to any depth. The beneficial influence of moxa, in relieving or curing 

 disease , apparently depends on its tonic action over absorption and 

 capillary circulation. Hence it should be employed in those cases only 

 in which there exists a state of debility of the capillaries and a con- 

 sequent retardation of their circulation, and a diminution of absorp- 

 md invariably avoided wherever there is increased action or 

 active inflammation." 



To hold the moxa over the part affected, an instrument has been 

 invented, but a portion of silver-wire formed into a loop, surrounding 

 the cylinder near the base, is sufficient. The moxa may be applied in 

 various ways. " It may be used so as not to cause any injury ; in a 

 greater degree, BO as to produce vesication ; and in a still greater degree, 

 an eschar, which may be either deep or superficial ; or it may be 



ARTS ANI> SCI. DIV. VOL. V. 



employed with the acupuncture needle." In the first form, it is burnt 

 near, but not in contact with, the part affected, and is often of 

 great service in healing indolent ulcers ; it generally requires to be 

 applied once a day. It is even used in some chronic inflammations of 

 the eye with very good effect. In the second form it is also to be held 

 near the skin, and continued till a blister results. In tic douloureux of 

 very superficial nerves this is sometimes beneficial. The third mode is 

 the most common, and for this the part to which the moxa is intended 

 to be applied is marked out, and the moxa being surrounded with a 

 piece of card-paper, which has been moistened with a solution of 

 common salt, to protect the adjacent skin, the moxa is ignited at one 

 end, and the combustion increased, if necessary, by means of a blow- 

 pipe. For the cure of obstinate sciatica and deep-seated diseases of the 

 joints a frequent repetition of the moxa may be required, but it seldom 

 fails to give relief. " When the moxa and acupuncture needle are 

 used together, a moxa of a proper size is to be perforated by a needle of 

 such a length as will be sufficient to reach the seat of the disease, and 

 at the same time extend so far from the surface of the skin as to keep 

 the moxa about one inch from it. The needle is then introduced, and 

 the moxa is now put in a state of combustion, and the heat disengaged 

 from it is communicated to the needle, and thence conveyed to the 

 seat of the disease." [ACUPUNCTURE.] When the pain from the third 

 mode of applying the moxa is very great, a linseed-meal poultice will 

 generally mitigate it, or liquor ammonia. 



Prejudice against this remedy, on account of its apparent severity, 

 has prevented its being extensively used, but almost all practitioners 

 who have made trial of it can attest its efficacy. It will rarely be had 

 recourse to, except in cases of a neuralgic or paralytic kind of such 

 obstinacy or painfulness as to justify the measure ; but in such diseases 

 it should not be overlooked. Its application has dispersed the almost 

 ossified nucleus of a goitre, which resisted all other means to effect its 

 absorption. (Wallace, On the Action of Moxa.) 



MUCAMIDE (C 12 H 12 N 2 12 ). This body is produced by adding 

 ammonia to mucic ether. It is a white crystalline substance, very 

 slightly soluble in boiling water. 



MUCATES. [Mucrc ACID.] 



MUCIC ACID (C lt S,0 lt , 2 HO). This acid is formed by the action 

 of dilute nitric acid upon gum arable, or sugar of milk, and some other 

 bodies. One part of sugar of milk is heated with 4 or 5 parts of nitric 

 acid diluted with half its weight of water; after effervescence has 

 ceased, the liquid deposits mucic acid on cooling. 



Mucic acid is a white crystalline powder, which is gritty between 

 the teeth : its taste is slightly sour. It dissolves in 6 parts of boiling 

 water, and the solution reddens litmus-paper. It is insoluble in alcohol, 

 and dissolves very sparingly hi dilute acids ; it dissolves in concentrated 

 sulphuric acid, imparting a crimson colour to it. When the mixture 

 is heated, charcoal is developed. When submitted to dry distillation 

 it blackens, and pyrmrmcic acid and other products are obtained. 



Mucic acid. 



= + 6HO + 2CO, + C 10 H 4 



Pyromucic acid. 



The alkaline mucates are soluble in water, whereas those which con- 

 tain an alkaline earth, or a metallic oxide, are insoluble. These salts 

 are all decomposed by the mineral acids : they combine with the base 

 and set the mucic acid free. Boiled with water mucic acid yields 

 the isomeric pa/mnmcic acid. 



MUCIN. A proteic substance found in crude gluten. 



MUCOVINIC ACID (C 10 H 14 10 ). An ethyl derivative of mucic 

 acid, bearing the same relation to that acid as sulphovinic acid holds 

 to sulphuric acid. [ETHYL.] 



MUCUNA PRURIENS, or COWITCH, the Medical uses of, will be 

 found under that head in NAT. HIST. DIV. 



MUDAR, the Calolropis Gigantea of Brown, and the Oalotmpis 

 miularii (Buch.), Asclepias yigantea of Linnaeus. Mudar is a plant 

 common in sandy places in many parts of India ; it has a milky juice in 

 its stem, which, as well as the bark of the root, enjoyed such reputation 

 among the native practioners as a medicinal agent as to lead to its use 

 among European practitioners in the East. It was found to be very 

 efficacious hi the cure of many obstinate cutaneous diseases, such as 

 lepra Arabum and elephantiasis : in syphilitic complaints also and 

 anasarca, it proved so valuable an alterative that it received the name 

 of vegetable mercury. Some use the powder of the bark of the root, 

 but Sir Whitelaw Anslie prefers the dried milky juice, which in a 

 recent state, if taken hi large quantity, is poisonous. It was thought 

 to possess some specific quality, but Dr. Duncan, by whom extensive 

 trials were made of it in Britain, showed that this is not correct, but 

 that it is infinitely more valuable from its common medicinal properties, 

 which correspond in every respect, according to him, both in kind and 

 degree, with those of ipecacuan. He even thought that, from the 

 facility with which any quantity could be procured from the province 

 of Bahar, the use of the Brazilian ipecacuan might be altogether dis- 

 pensed with in our East Indian settlements. 



Besides its practical value as a medicinal agent, the bark of the root 

 possesses the singular property in one of its constituents, Mudarine, of 

 being very soluble in cold water, gelatinising when the solution is 

 heated to 85 or 90 Fahr., and recovering its fluidity on cooling. It 

 is almost the only instance known of any organic body being an ex- 



So. 



