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"It appears not unlikely that many of the so-called chemical elements may prove to be compounds of helium, or, in other words, that the helium atom is one of the secondary units with which the heavier atoms are built up. In this connection it is of interest to note that many of the elements differ in their atomic weight by four-the atomic weight of helium.

"If the a particle is a helium atom, at least three a particles must be expelled from uranium (238.5) to reduce its atomic weight to that of radium (225). It is known that five a particles are expelled from radium during its successive transformations. This would make the atomic weight of the final residue 225-20=205. This is very nearly the atomic weight of lead, 206.5. I have for some time considered it probable that lead is the end or final product of radium. The same suggestion has recently been made by Boltwood."

Then follows a discussion of the evidence on which this suggestion is based.

I think that the above quotation makes my position clear on this subject. E. RUTHERFORD.

McGill University, Montreal, October 11.

Radium and Geology.

THE Hon. R. J. Strutt has advanced weighty reasons in favour of supposing radium to be confined to a certain shallow layer over the surface of the earth. To assume, however, that a heavy element is thus restricted in distribution appears to me to present difficulties. It would appear that an a priori probable reason why uranium should disintegrate more rapidly near the surface than at greater depths would bridge over the difficulty, and, if for that reason only, would deserve attention.

I think such a reconciliation of observational facts with the probabilities involved would be found in the view that the break up of uranium is not entirely spontaneous, but is partly secondary in character, i.e. that disruption of an a particle from an unstable atom may precipitate the failure of neighbouring atoms, as Prof. J. J. Thomson has suggested might happen in the case of radium. If this be the case, and we assume that the uranium is in general distributed in random aggregates throughout the earth, a reason is at once forthcoming for Mr. Strutt's results. The lighter constituents in the outer aluminium, silicon, oxygen-exert a lesser screening action than the heavy metals deeper down. The conflagration is, as it were, isolated where the heavier metals interpose to absorb the energy of the a ray which initiates the changes leading to radium. It is probable that if the absorption is adequate to reduce the kinetic energy below a certain critical amount, there would be no propagation of disruption.


The remarkable fact observed in Mr. Strutt's experiments that radium is more abundant in the heavier silicates of plutonic rocks than in the lighter is not opposed to this view, but rather in keeping with it; and the absence of detectable radium in metallic meteorites need not be occasioned by the absence of uranium, but by the slower breakdown of the latter.

I cannot claim to speak authoritatively on the literature of this subject, but I can recall no other experiments bearing on this matter than those quoted by Prof. Rutherford in the last edition of his Radio-activity." The case of uranium does not appear to have been investigated. Prof. Rutherford records an experiment in which he dissolved some pure radium bromide in 1000 times its bulk of a solution of barium chloride, and found no change in the 7 radiation. I venture to suggest that this experiment is not conclusive. Increasing the volume 1000 times increases the average distance of the molecules but ten times, even were these fixed in the medium. This leaves the intervening distances still of the order of millionths of a centimetre. The heaviest metal brought to such tenuity would exert no appreciable screening influence, even from the a rays, to say nothing of more penetrating radiations. Mr. Eve's experiments, which are also quoted by Prof. Rutherford, are not, I think, to the point.

As cosmical effects of the greatest interest are involved, I think the question of how far radio-active effects are

spontaneous deserves full investigation, and I think more especially with regard to the primary step, the generation of radium from uranium. If this is dependent on the matrix and on concentration, entirely new considerations arise.

It is not impossible, in the present meagre state of our knowledge, that the penetrating radiations observed at the surface of the earth have to do with the genesis of radium from uranium, the failure of such rays to penetrate deep into the crust limiting the production. The suggestion is continuous with that advanced above. J. JOLY.

Geological Laboratory, Trinity College, Dublin.

IN reply to Mr. O. Fisher's interesting letter of October 11 in this Journal under the above heading, it may be suggested that, though a state of stable thermal equilibrium exists now in the earth, it did not in the past, and that the earth has cooled down from a great initial temperature. We are, however, met with this difficulty, that the movements of the crust have been enormous in late geological times, as shown in the great mountain ranges of Tertiary date. This seems to be a fact entirely antagonistic to the suggested explanation.

No doubt some of the current geologico-dynamic theories will go to the wall should Mr. Strutt's interesting researches be confirmed, but I am of opinion that his work will ultimately prove helpful to sounder ideas of the origin of earth structure. T. MELLARD READE.

Park Corner, Blundellsands, October 13.

THE age of the great mountain ranges mentioned above by Mr. Reade, though comparatively late, is much earlier than that of the changes of vertical level investigated by Prof. Hull and Dr. Spencer to which I referred. They are evidenced by the drowned plains bordering the Atlantic on both sides, and by the deep cañons in them which are the continuations of existing river channels. These changes of level are considered to be of Pliocene or early Pleistocene Godwin date, and, therefore, geologically very recent. Austen came to a similar conclusion about the English Channel.

I thank Mr. Strutt for noticing (p. 610) my letter in NATURE of October 11. The fact of uranium not having been recorded in analyses of the rocks, as referred to by Mr. Strutt, has occurred to myself, but not being a chemist I have not alluded to it. But it seems to me that there ought to be an appreciable store of uranium present, large in proportion to the radium it is producing, if the latter is not permanent. That there is not appears to indicate that the disintegration of the radium, and therefore the escape of heat from it, is in some way checked in the earth's crust, as suggested by Mr. Rudge in his letter to the Times of August 18, and that consequently the temperature gradient is not due to radium in the crust, but to the cooling of the interior. I think it is in this direction that we must seek for a reconciliation between radium and geology. Graveley, Huntingdon, October 19. O. FISHER.

Meteorological Data.

I SHALL be glad if you will enable me through your columns to make known to those interested in the collection of meteorological data the following information.

A number of copies of the Cape of Good Hope Magnetical and Meteorological Observations, vol. ii., "Meteorological Observations, 1841-6," have been placed at my disposal by the Controller of H.M. Stationery Office for distribution. The volume contains hourly observations, for each day, of pressure, temperature, and humidity, with a journal of other meteorological data.

I shall be glad if any scientific institution or library which desires a copy will be good enough to communicate with me upon the subject at the Meteorological Office, 63 Victoria Street.

I have also available for distribution in a similar manner

a few copies of the following works:

"Meteorological Observations taken during the Years 1829 to 1852, at the Ordnance Survey Office, Phoenix Park, Dublin, . . . and Other Places in Ireland."

"Abstracts from the Meteorological Observations taken at the Stations of the Royal Engineers (including 15 Colonial Stations) in the Year 1853-4, with Notes on Meteorological Subjects."

"Abstracts from the Meteorological Observations taken at the Stations of the Royal Engineers (comprising 13 British and 18 Colonial Stations) in the Years 1853-4, 1854-5, 1855-6, 1856-7, 1857-8, and 1858--9."


Abstracts from the Meteorological Observations taken in the Years 1860-61, at the Royal Engineer Office, New Westminster, British Columbia."

These volumes will be issued without payment.

I may also mention at the same time that the Meteorological Committee, acting in accordance with the recommendation of the fourth International Conference on Scientific Aëronautics, has undertaken to subscribe for a number of copies of the international publication of the observations of the upper air on the "international days," which will be issued by Prof. Hergesell, the president of the commission. I shall be glad to know whether any scientific institution or library wishes to subscribe for a copy of this publication. The amount of the subscription is il. per annum. W. N. SHAW.

The Breeding Habits of the Tsetse-fly.

I SHOULD be greatly obliged if you could find space in your columns for the following extracts from a letter which I have received from my friend Dr. A. G. Bagshawe announcing the discovery, I believe for the first time, of the pupa of the tsetse-fly (Glossina palpalis) in nature. As this species of fly is now known to be the agent which disseminates the infection of sleeping sickness, any discoveries relating to its breeding habits are of the utmost importance from the point of view of devising measures for extirpating the fly or checking its increase. Together with my colleagues Lieuts. Gray and Tulloch, I spent a great deal of time, when I was in Entebbe, in searching for the pupa of the fly, and we offered the native boys a rupee each for them, but all our efforts to find them in nature were unsuccessful, although captive flies deposited great numbers of pupæ in our cages. I ought, perhaps, to explain at this point that the tsetse-fly is viviparous, and produces a full-grown larva, one at a time; the larva is of a light yellowish tint when born, and wriggles about actively for an hour or so, and then turns in a short time to a dark brown pupa, about the size of a grain of wheat.

Dr. Bagshawe, who is already well known for the botanical collections he has sent home, has succeeded where we failed, and as I do not know what steps he has taken to secure the priority for this most important discovery, I hasten to make it public on his behalf. It will be seen that the pupæ have been found in the banana plantations. Since bananas are the staple food of the Baganda, it would be impossible to destroy the plantations without creating a famine. I may mention, however, that we found the tsetse-fly swarming on the deserted island of Kimmi, on the Victoria Nyanza, where there were no plantations, so that this is perhaps not its only breeding place.

E. A. MINCHIN. Lister Institute of Preventive Medicine, October 17.

(Extract from Dr. Bagshawe's Letter.) "On August 29 I got them [the pupa] at last. I had marked down a particular spot as likely, and had pitched my camp near by to search. Along the lake shore for about 100 yards was a belt of bananas 10-20 (40?) yards in width, and behind that undergrowth, going back 100 yards or more. Fly were thick and bothered one up to

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on the assumption that a fly with five legs is as good as one with six, and if one snipped off a piece of a known l-g that fly could be identified when caught again. Six series of experiments could be made. It worked admirably. The experiments want repeating on a larger scale (I hope to do it on the Semliki), but I have shown clearly that the range is at least a mile. This is the reason why the breeding places have eluded search so long. (Signed) ARTHUR G. BAGSHAWF Albert Edward Lake, September 1, 1906."

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Suspended Germination of Seeds.

IN Mr. Claridge Druce's letter in NATURE of October 11 he rightly remarks that in order to prove the suspended germination of seeds over long periods, instances are required in which the factors of wind-carried seeds, &c., can be with some certainty eliminated. The following case, though not absolutely conclusive, may still be of interest

Personally I am of opinion that the seed of Digitalis does preserve its germinating power for a considerable time. A few years ago I cleared a space, speaking from memory. of say forty yards by thirty yards, occupied by old Portugal laurels 25 feet to 30 feet high, planted fully sixty years ago, with Rhod. ponticum lining the path in front; the space, except on the path side, is surrounded by thick coverts. The nearest growing foxgloves were to the west along a 6-feet path running parallel with the long side of the cleared area, and distant, say, ten yards; both sides of this intervening space are lined by old rhododendrons. seed blown along would fall on the path or the edge of the clearing. The laurels were removed in January and February, when all, or nearly all, the seed would have been shed. Notwithstanding this, the next spring the whole of the cleared ground was covered with a uniform carpe of seedlings, practically hiding the bare ground. It seem> to me that, even if some wind-blown seed penetrated the evergreen barrier, the seedlings would have appeared in patches.

I have known many other somewhat similar instances, but none quite so specialised as the above. I may add tha the spot is exceptionally protected from wind, having tali forest trees on all sides. ARCHIBALD BUCHAN-HEPBURY.

Smeaton-Hepburn, Prestonkirk.

Biometry and Biology.

OWING to the proof of my letter in last week's NATURE reaching me too late for careful revision, one or two slips escaped notice. Of these, I would wish to direct attention to the interchange of the words intra-racial and inter-ract in the second paragraph on p. 609 (column 1, line 14). KARL PEARSON. Biometric Laboratory, University College, London, October 19.


HE Salisbury railway accident, being followed
after no very long period by the somewhat
similar disaster at Grantham, undoubtedly raid.
feeling of considerable uneasiness in the public mind.
The recent publication by the Board of Trade
Major Pringle's report on the former calamity shoul
do something to allay this apprehension, if only he
cause it shows that the cause of the derailment o
the train was not "mysterious," but is fully to h
explained. That the evil we know is less alarming
than one which vaguely threatens is a fact for wh
we have classic authority.

The accident occurred on July 1 at the Salisb Station of the London and South-Western Rails n the train being the special boat express from Plyme to London, carrying passengers who had arrived the American liner New York. The train consist! of four eight-wheeled vehicles hauled by a fem

coupled engine with a leading bogie, having an eightwheeled bogie tender. The coaches were not of excessive length, the longest being 48 feet, and all were on bogies; the engine was one of the company's usual modern express type, and although the boiler is mounted higher than was formerly the practice, the train was well calculated to run safely round curves under usual conditions: yet it was a curve that caused the accident. In saying this we are not verbally in agreement with Major Pringle's report or with the verdict of the coroner's jury at the inquest on the unfortunate victims, both of which attribute the accident to excessive speed. No doubt the speed at which the curve was taken was too high, but if the curve had not been so sharp the speed would have been perfectly safe; in fact, it was the curve which was the abnormal feature, the speed being ordinary for ordinary conditions. It may seem like splitting hairs to cavil over terms in this manner, but the matter has greater significance than may appear. If we allow the accident to have been due simply to speed, then the railway authorities have done all that they can do when they order driversas they always have done-to reduce speed to within safe limits; but if it is stated that the accident was due to excessive curvature of track, then the company will appear not to have done all that is possible until they flatten the curve. Whether the danger warrants the expenditure is another matter, but we may remember that so long as drivers are human and liable to err, the chance of disaster is always present whilst such an abnormal curve exists on a main line over which, express trains run; in other words, if the Salisbury curve did not exist accident from the same cause would be impossible.

Speed is always a doubtful point in the elucidation of the cause of accident, but there is no doubt, from the evidence at the inquest and the Board of Trade inquiry, that the train was travelling very greatly in excess of the thirty miles an hour laid down by the regulations as safe for the curve immediately to the east of Salisbury station. One witness estimated the speed to have been as high as seventy miles an hour, and Major Pringle considers that possibly this may not have been an extravagant estimate. When the engine

and tender left the line it came into violent contact with a milk train moving on the down line, and the wreckage also struck a light engine standing in a bay close by. Particulars of the loss of life have been fully published, and it will be sufficient to say that on the express twenty-four passengers were killed, seven were seriously injured, the engine-driver and fireman were killed, and a ticket collector and two waiters on the dining car were injured. The guard of the milk train and the fireman of the light engine were also killed, and the driver was badly scalded. The chief interest of Major Pringle's report, as in all reports of this nature, centres in his conclusion as to the probable cause of the accident. Speaking at large, there is no doubt, as we have stated, but that the disaster was due to high speed on an awkward curve, and the evidence all points to the fact that the engine and tender turned over bodily; how the forces set up acted so as to bring about the result is the problem that remains to be solved.

According to the plan of this part of the line, given in the report, the up line is straight through the station, but at the eastern end of the platform a curve to the left of ten chains radius (compound) extenis for a distance of about ninety-two yards. In the body of the report is a statement attributing a radius of eight chains to the curve, this representing the sharpest part of it. There is a rising gradient of I in 158, and the maximum superelevation on the

curve is 3 inches. It was on this part of the line that the accident occurred, the overturned engine being found at the termination of the curve, and just in front of facing points with reverse curves of 7 chains radius; naturally there could be no superelevation at the points. The report states that the three leading vehicles of the express were overturned in various directions, the frames stripped of woodwork and completely destroyed. The fourth vehicle fared little better. Comparatively little damage was done to the last vehicle, which came to rest in an upright position, with the last pair of wheels on the proper rails. The engine and tender were both overturned on their right sides, but less damage was done than might have been expected, and the engine was shortly afterwards hauled to Nine Elms on its own wheels. Five vans of the milk train were completely destroyed, and five were damaged. This destruction of rolling-stock was accompanied by remarkably little damage to permanent way on the up line over which the express was running, but a length of about forty yards of the down line was torn out and destroyed.

The weight of the engine was nearly 54 tons (53 tons 19 cwt.), 16 tons 17 cwt. being on the leading bogie, 19 tons 2 cwt. on the leading driving axle, and 18 tons on the trailing axle. The tender weighed 44 tons 17 cwt., 23 tons 2 cwt. being on the leading bogie, and 21 tons 15 cwt. on the trailing bogie. The centre of gravity of the engine was calculated at about 5 feet above the rail-level, and that of the tender at about 4 feet.

So far we have most of the chief data generally at command for calculating what would be the limit of safe speed for travelling over the part of the line where the accident occurred. Calculations for the centre of gravity of an engine are somewhat tedious, even when all data are at command, and the figures given appear somewhat low for an engine of the type. In former days this would have been of less consequence, but the tendency to raise the boiler, so that the chimney becomes nothing more than a 'frill round a hole "-as a railway engineer recently said-makes the centre of gravity a factor that needs the modern high boiler is far more apparent than more attention, although the effect in this respect of



It is unfortunate that our chief railways were designed for lower speeds than are now required, and altogether for more primitive conditions; thus it is possible that when Salisbury Station was built it was not anticipated that a train would ever run through, and the curve of 8 chains would be without danger for a stopping train.

Major Pringle says that the engine in question, with a centre of gravity 5 feet above the rails, when traversing a curve of 8 chains, would be in unstable equilibrium at a speed of about sixty-seven to sixtyeight miles per hour, even if full allowance were made for the beneficial effect of 3 inches superelevation. Major Pringle does not give his calculations, but, as he says, the result may be taken as agreeing WV2 with modern formulæ. The rule = E, where 125 R W= width of gauge in feet, V-velocity in miles per hour, R=radius of curve in feet, and E-elevation of outer rail in inches; or if the speed V were expressed in feet per second the formula would become W V2/gR, where g is If the formula were 32.2. used to calculate the superelevation for a speed of sixty miles per hour, it would give superelevation of 25.6 inches; on the other hand, at the speed of thirty miles an hour-that laid down as a maximum by the railway company's engineers-the rule would give

superelevation of 6.4 inches. The maximum superelevation on the South-Western Railway is 6 inches, and it is, of course, altogether impossible to work with any such superelevation as more than 2 feet. It will be understood that the whole of the constraining force required to keep the engine moving in the curve is supplied by the resolved component of the weight of the engine acting parallel to the plane of the radius towards the centre of curvature.

It will be evident, therefore, that superelevation is a remedy of limited efficacy for a serious defect. The centrifugal force at sixty miles per hour (a speed that the evidence of figures shows to have been exceeded, but which we adopt as a convenient standard) would be _54 × 882 or, approximately, 24 tons (24′597). 32'2 × 528' The accompanying diagram (Fig. 1) illustrates the resultant of the two opposing forces acting on the engine.

M=centre of gravity of the engine 5 feet above raillevel. The line MQ-the weight of the engine, and MF = the centrifugal force at sixty miles an hour to the same scale. Completing the parallelogram MFRQ, then MR the resultant of the two forces. Producing MR, it cuts the rail-level at the point H, which is 5.29 inches inside the outer rail; AE is the superelevation. There would only be, therefore,

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The above gives a very nearly correct result when the point H is in the neighbourhood of C, as it should be. The error increases as H approaches A.

We may compare the value of CH obtained by the two methods; we have already shown by the exact method that CH=23 inches. Applying the approximate formula CH=23.6 inches.

From the foregoing calculations it would appear that if the train were travelling at a speed of more than sixty-six miles an hour the engine would turn over sideways, but it will be understood that deductions drawn in this way are not proof, though they may be evidence, of what has occurred. The speed of the train is, of course, a very indeterminate quantity; the maximum superelevation was, as stated, 3 inches, but, to judge by the plan, this did not extend on the curve for a greater distance than about 50 feet, and it would appear that at the spot where the trouble commenced (to judge by the damage to the line) the superelevation was somewhat less. Again, in placing the position of the centre of gravity of the engine, there are various unknown factors which it would be necessary to take into consideration to enable a true result to be reached; for instance, there is the unequal compression of the springs causing lateral displacement of the centre of gravity, rush of water in the boiler, and the extent of wear of wheels and rails.


ESTIMATION OF BLOOD-PRESSURE. HE subject of blood-pressure is one of great THE interest both to the physiologist and the clinical physician. By blood-pressure is meant the pressure which the blood exerts on the interior of the hart and blood-vessels, but it is chiefly with the vascular blood-pressure-arterial, capillary, and venous •hat the physician deals. Our conception of intravasculor pressure is facilitated by considering what happens when an aperture is made in an artery, capillary, or vein of a living animal. In the case of the artery the blood squirts out with considerable force, the height of the jet measuring the pressure exerted on the interior of the vessel. Experiment shows that the pressure falls slowly from the heart to the region of the smallest arteries, or arterioles, where there is a considerable fall, the pressure in the capillaries and

veins being comparatively low; in the large veins opening into the right heart it may, indeed, be minus, owing to the suction action of the thorax, and hence when these veins are cut air may actually be sucked into the blood-stream.

The vascular blood-pressure is subject to considerable variation both in health and disease, and it will readily be seen that its accurate estimation is of great clinical value. To take an illustrative case. In certain poisoned states of the blood the small arteries undergo considerable contraction; in consequence of

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methods is available for clinical purposes. Recently, however, a method has been devised in which the employment of the knife can be dispensed with, and one, moreover, yielding results quite as accurate as those just referred to. It consists in enveloping some part of the upper extremity-arm, forearm, or fingerin a gutta-percha bag, and connecting the latter, by means of a tubing, with a manometer. The bag is blown up until the pulse on the distal side of it is obliterated, the pressure then registered by the manometer representing the systolic," or obliterative pressure. The "diastolic " pressure, or that obtaining between the heart beats, is measured by noting the excursions of the manometric index produced by the pulsations of the artery; it is held that the maximum movements occur when the pressure


50 40 30

FIG. 1.-Dr. George Oliver's Hæmomanometer (reduced to half size). A is the graduated glass tube along which moves the coloured spirit-index, represented by the dark curved line at the right-hand bend; B is the open end on to which fits the rubber tube communicating with the enveloping bag, or armlet; c is kept closed by means of an air-block, while the blood-pressure is being taken.

this the blood cannot pass into the capillaries and veins with its wonted facility, and tends to be dammed back upon the large arteries and heart; in other words, the blood-pressure rises in the left ventricle and in the whole arterial tree proximal to the contracted area, and this heightened pressure is further augmented by an increase in the force of the heartbeat, called forth by the necessity to overcome the increased resistance. An increased strain is thus put upon the heart and arteries, and this, if long continued, may lead to disease in them; and in this way such serious affections as aneurism, heart-disease, and apoplexy may be brought about. The importance of early detecting such cases of augmented pressure is apparent, in that it enables steps to be taken to correct the underlying faulty condition

of blood, and thus to ward off grave consequences.

Until recently the physician had to be content to rely upon his sense of touch in estimating blood-pressure, and thus it was that the older physicians spoke of a "hard" and a "soft" pulse, the former indicating a high and the latter a low bloodpressure. More modern physicians describe the pulse as compressible" or "incompressible," or the vessel as being in a state of high or low "tension," according to the readiness with which it yields to the pressure of the finger. This tactile method is, however, far from trustworthy. Not only


on the artery is just sufficient to balance the diastolic pressure.

Hitherto the manometer most frequently used in these observations has been the ordinary mercurial one; but Dr. George Oliver, of Harrogate, has recently devised an instrument which is not only more handy, but would appear to give more accurate readings than the mercurial manometer. It consists of a fine bored glass tube (Figs. 1 and 2) which during use is kept closed at one end, and connected at the

is long experience needed to acquire FIG. 2.-Method of employing Dr. Oliver's hæmomanometer.

A is the bæmomanometer; Dis the armlet; c is the rubber tubing connecting the armlet with the glass tube; B is the rubber ball for inflating the armlet; this is provided with a screw (covered by the thumb), by means of which the armlet and tubing may be gradually deflated.

even moderate efficiency in it, but from a variety of causes the most skilful are liable to make false estimates by its means; nor do the findings admit of accurate record. In short, though useful as a roughand-ready method, it lacks the precision needful for scientific observation.

The earliest method of estimating the arterial blood-pressure consisted in cutting the artery of an animal and observing the height to which the blood was forced out. Later the more delicate plan was adopted of connecting the interior of the vessel with a mercurial manometer, by means of an elastic tubing filled with saline solution. Clearly neither of these

other with the enveloping bag by means of elastic tubing. A minute drop of coloured spirit introduced into the glass tube serves as the index. At the commencement of an observation the index is at zero, which is situated at the open end of the tube. As the bag is blown up the index is driven onwards, compressing the air in front of it, and advancing with every increment of pressure. The instrument is readily graduated by means of a mercurial manometer. It will be seen from this description that the

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