Chapter LIV: Diseases Due to Working in Compressed and Stagnant Air

_Caisson Disease._

Caisson disease, or compressed air illness, is a product of modern civilisation. It seizes labourers who are engaged in sinking mines, in excavating the beds of rivers to obtain a foundation for the piers of bridges, and in tunnel making. A caisson is a cylinder composed usually of iron plates riveted together to form a shaft, which, in the case of bridge building, is sunk into a river, for example, so that its open mouth shall rest upon the bed of that river. Down this shaft, when it is properly closed at the top by a perfect fitting diaphragm, men descend, air having been previously driven in under considerable pressure to drive the water out at the bottom of the cylinder and to keep it out. The workmen enter and leave the caisson by a chamber or “lock” close to the diaphragm at the top. The length of the caisson shown in the diagram made for me by Mr Huntley, engineer at the Redheugh Bridge on the Tyne, is 90 feet, and at the time this drawing was made the men were working 77 feet below high-water level mark. In building a caisson it is the lower part that is made first. Thirty feet of circular iron plates are riveted together, care being taken to make the bottom bell-shaped. Before this unfinished caisson is lowered on to the bed of the river, there is placed outside of it a larger cylinder, and the two are united at the rim of the bell-shaped expansion. The space between the two cylinders is filled with cement. Successive lengths of twenty feet of cylinders are added, and subsequently the air lock, or the chamber by means of which men enter and leave the caisson. Two men work as a rule in each caisson, but this number varies with its size. In the lock there is an inner as well as an outer air-tight door, both of which open towards the interior of the caisson. When a labourer has to enter the cylinder that is filled with compressed air, he passes into the workman’s part of the lock by the door A (see Diagram); the other door, B, which opens into the main shaft, is at this time perfectly closed, and kept thus by the great pressure within the caisson. Once he is in the lock and door A closed, also the outlet cock C, the inlet cock D is gradually opened. By degrees the compressed air of the cylinder escapes into the lock, and when the pressure inside the lock comes to equal that inside the cylinder, door B opens of itself. The labourer now enters and descends the internal cylinder by means of a ladder to his work on the bed of the river. On leaving the caisson the process is reversed. The men, while working inside the caisson, shovel the soil and stones into large iron buckets which, when filled, are raised by a chain wound by an engine outside the cylinder. This chain passes through the “material” part of the lock, the sliding doors and cocks of which are moved by men outside who operate very quickly. As the excavation proceeds, the cylinders sink by their own weight and require new lengths to be added, bars of pig-iron being thrown into the space between the external and internal shafts so as to favour the sinking of the caisson.

It was a French engineer, M. Triger, who first employed caissons in order to reach a bed of coal that lay underneath the River Loire. Subsequently he used them for boring wells and fixing piles for bridges. From the first day on which caissons were used, the workmen have complained of pains in their ears and joints. In making the Blackwall Tunnel, several of the men were ill. Dr Snell, the surgeon to the Blackwall Tunnel, has embodied his experience in an excellent monograph. It is to MM. Pol and Watelle we are indebted for the earliest account of the pathological effects of compressed air upon men working in a mine at Douchy in France. Of 64 workmen exposed to the influence of compressed air, 47 stood the work well, 25 gave up their employment, and 2 died. The risks incurred are not so much when the men are at work in the caisson as on _entering_ or _leaving_ it, _i.e._, when they are passing through the lock undergoing _compression_ before entering the cylinder, or coming out through the lock and undergoing _decompression_. Of these two, decompression is the more dangerous. If this is not accomplished slowly, the individual may not only experience very unpleasant symptoms, he may become the subject of permanent ill-health. It is because, in our daily life, the ordinary atmospheric air is pressing upon us _equally all round_ that we are unconscious of the 15-lb. pressure to the square inch exerted upon our bodies, also that when we dive under water we are unaware of any superincumbent weight. Engineers have utilised knowledge of these facts, and have tried to imitate nature by subjecting men to pressure equal to two, three, or four atmospheres, or in other words to weights equal to 30, 45, or 60 lbs. to the square inch.

In this country caissons were first made use of by Hughes in 1851 to make a bridge at Rochester over the Medway. Brunel subsequently employed them at Chepstow and at Saltash. At Saltash one of the men died shortly after emerging from the caisson, wherein he had been working at a depth of 87.5 feet below the surface, and under a maximum pressure of 40 lbs. During the building of the bridge of Kaffre Azzyat over the Nile in 1859, five Arabs died from the effects of compressed air. Blood issued from their mouth, nose, and ears. These men had been working at a depth of 85 feet below high-water level mark, and under a pressure of 34 lbs. to the square inch. For several years now, wherever an important bridge has had to be built, caissons have been used. It was thus that the foundations were obtained for such structures as the railway bridge across the Rhine at Strasburg, the Forth Bridge, and the Suspension Bridge at Brooklyn, New York. Descriptions of the illnesses that occurred among the workmen engaged at the Forth Bridge, and at Brooklyn, have been embodied in monographs by Dr James Hunter, in his M.D. Thesis for Edinburgh University, and by Dr Andrew Smith of New York. At the Brooklyn Bridge the pressure varied from 18 to 36 lbs. to the square inch above that of the atmosphere, and the caissons were lighted by gas. Ventilation of the cylinders was attended to as far as possible, but, notwithstanding this, the air frequently contained as much as 0.3 per cent. of carbonic acid as against 0.06, which is regarded as the maximum for a well-ventilated space. Into the caissons 150,000 cubic feet of air had to be pumped every hour to satisfy the respiratory requirements of the labourers. The men worked in two shifts of four hours, separated by a period of rest for two hours, but as the cylinders sank deeper and deeper the working time had to be correspondingly diminished. Dr Smith treated 110 cases of compressed air illness, of which three proved fatal.

In the following brief account of the signs presented, and the symptoms complained of by one of the patients who was under my care in the Newcastle Infirmary, will be found a recital of the details of caisson disease. The man was a sinker, forty-five years of age. He was working in the caissons at the Redheugh Bridge close to the Infirmary, 77 feet below high-water level mark, at a pressure of 31–35 lbs. to the square inch. On leaving work one day he felt numb in his legs, became sick and vomited; shortly afterwards he became giddy and fell to the ground unconscious. His comrades carried him home, where he lay for twelve hours in a state of unconsciousness. When he came to himself he complained of pains all over his body, incomplete loss of power in his legs, headache, and buzzing in his ears. Next morning on getting out of bed his nose began to bleed, but as epistaxis is common among sinkers, he thought lightly of the matter and attempted to go to work. He again lost consciousness for a brief period, and it was in this condition that he was brought to the Infirmary. Subsequently he complained of severe pains all over his body, difficulty of breathing, a feeling of sickness, and profuse perspiration; the pulse was slow and full, there were muscular rigidity, loss of power in his legs, and deafness. The urine was free from albumen and sugar. During the day there was occasionally delirium of a noisy character. Heart, lungs, liver, and spleen seemed healthy. When a few days afterwards the symptoms which have already been detailed had subsided, and the patient attempted to walk, it was observed that there was considerable staggering, and that he tended to fall forwards. On examining his blood microscopically, nothing abnormal was detected beyond the fact that the coloured cells were slightly paler than usual, and did not form rouleaux properly. It was several weeks before patient could walk well, also before he lost the noises complained of in his head, and that his hearing was perfectly restored. During his stay in the Infirmary he had spitting of blood on a few occasions.

At the Forth Bridge, Hunter found that several of the men who worked in the caissons suffered from bleeding at the nose. It is gratifying to know that not one of his cases of compressed air illness proved fatal. The men worked under a pressure of from 15 to 34 lbs. above that of the atmosphere, and from four to six hours at a stretch, but as the caissons sank this was found to be too long. It was observed that the men suffered most in their general health when the soft silt in the bed of the river containing decomposing organic material was being removed.

One of my clinical clerks[156] volunteered to enter a caisson. He observed that the candles burnt more quickly in compressed air than in the ordinary atmosphere, and that as a consequence there was much more smoke. His breathing was at first quickened (40 respirations instead of 16 to the minute), while in the case of Mr Huntley, the engineer who accompanied him, and who was accustomed to the position, the respirations were only 20 to the minute. The pulse-rate was also quickened. Mr Fawcus experienced very unpleasant sensations in his ears, which gradually abated when he swallowed air, and thus inflated the middle-ear through the Eustachian tube. He could speak easily enough, but he could not whistle. There was no difficulty of breathing, although the pressure in the cylinder was 41 lbs. to the square inch; nor was there any sense of fatigue, but rather a feeling of fitness. Another of my students on emerging from the caisson had bleeding at the nose, severe earache and faceache. Pain and unpleasant sensations in the ears are complained of by nearly all on emerging from a caisson for the first time. The pain is apparently a mechanical effect, and is the result of the drum of the ear being forcibly driven in by the compressed air; for when a workman has acquired the faculty of swallowing air and passing it from his throat up the Eustachian tube into the middle-ear, so as to equalise the pressure, the sensation is no longer felt. Under these circumstances, it is unwise for any person who is suffering from a cold in the head or naso-pharynx to enter a caisson. The conditions inside the caisson are unnatural. As the whole body is subjected to an enormous pressure, men can only work therein for a short period at a time. It is a well-known fact that in the ordinary affairs of our daily life, some of our best work is done when we are working under mental pressure; and while the simile does not actually hold good of comparing mental with physical work, also of comparing physical work done under normal and abnormal pressure, yet experience shows that in the caisson the workmen, instead of feeling any bad effects from the compressed air, are so buoyed up by it, that in a given time they do far more and much harder work than when they are on the surface. Besides, as they are unconscious of putting forth extra effort, they do not feel fatigued, they perspire freely, and are apt to rub themselves incautiously, thus causing skin eruptions. Just as candles burn with greater rapidity inside the caissons, so too, it would appear, are the vital processes in the workmen quickened, disintegration of their tissues hastened, and the functions of the eliminating organs heightened. This simply means that all round more work is done by, and more waste formed in, the human body. Unless a caisson suddenly ruptures, as occurred a few years ago in France, the men when working inside run very little danger. It is on emerging from the cylinder, _i.e._, when he has undergone decompression, that the workman runs the risk of becoming giddy, and of being unable to stand, of having temporary paralysis of the legs, of experiencing muscular pains, called “bends,” all over his body, but particularly in legs and back, of suffering from bleeding from the nose, ears, and lungs, or of becoming unconscious.

That pressure _per se_ plays a part in the production of the symptoms is shown by the fact that as the caisson sinks and the internal pressure is correspondingly raised, the men suffer correspondingly. On the Tyne the men always suffered more when the pressure inside the cylinder was increased so as to keep pace with the rising tide. The condition of the air inside is also of importance. As more smoke is given off by the candles, and the men work harder inside than outside the caissons, the air is rendered very impure. At the Brooklyn Bridge each man was supplied with 1000 to 3000 cubic feet of air per hour, and yet the air inside the cylinders contained as much as 0.3 per cent. of carbonic acid as against 0.06, which is considered a healthy average. It is desirable that the workmen should have not less than 6000 cubic feet of air per hour. At the bridge on the Tyne, where my patients worked, 3000 cubic feet of air per hour were at first supplied to the workmen, but after their breakdown in health, this amount was raised to 5000.

It is difficult to say what amount of atmospheric pressure men can endure with safety. With the object of throwing light upon this subject, experiments have been conducted by Hersent, a French engineer at Bordeaux, and also by Dr Lepine. Hersent tried the effects of compressed air both upon dogs and men. Some of the dogs on leaving the caisson, others the day after having undergone decompression, became paralysed in their limbs. Men similarly treated suffered from severe pains in their limbs and itchiness of their skin. Lepine experimented with guinea-pigs and rabbits. When these animals had undergone rapid decompression after exposure to the influence of compressed air, they became paralysed in their hinder extremities, convulsions supervened, followed by death in a quarter of an hour. On making a post-mortem examination of the bodies, the central canal of the spinal cord was found to be distended by gas which had torn its way into the canal. There were also gaseous bullæ around the blood-vessels of the spinal cord. Several of the small arteries were torn and had bled. In one case where the animal died on the thirteenth day after exposure to compressed air, followed by rapid decompression, Lepine found foci of softening in the anterior horns of grey matter of the spinal cord due to gaseous emboli and to hæmorrhagic infarction or rupture of blood-vessels.

There is a very great tendency for grave accidents to be produced in man when the pressure in the caissons exceeds four to five atmospheres. The greatest risk occurs when the workmen are coming out of the cylinders and are in the lock undergoing decompression. If decompression is effected suddenly, harmful or even fatal results are likely to ensue. One minute for every three pounds of pressure is the time usually given for decompression, or five minutes for each atmosphere, but it is obvious that the longer the labourers are in the caissons and are exposed to very high pressure, the greater is the probability of a larger amount of gas being dissolved in the blood and the greater the time therefore required for decompression.

A caisson has been known to burst. This causes the most sudden decompression possible. It is almost always a fatal accident owing to the rapid disengagement into the tissues of the nitrogen gas of the atmosphere which had been dissolved in the blood of the workmen under very great pressure. Death is often preceded by convulsions. If the workmen rally, their legs are found to be paralysed; this loss of power may be temporary or permanent.

Three theories have been brought forward to explain compressed-air illness: (1) carbonic acid poisoning; (2) mechanical congestion of internal organs; (3) increased solution by the blood of the gases in the cylinder and the sudden liberation of these gases from the blood into the tissues during decompression.

If caisson disease were due to carbonic acid poisoning, we would naturally expect the symptoms to show themselves during the time the men are working in the cylinder, and not after they leave it. Dr Andrew Smith of New York believes that the illness is the result of mechanical congestion, especially of the brain. In several of the men who died the membranes of the brain were found to be deeply congested, a pathological condition that doubtless contributed to the fatal termination.

My own opinion is that caisson disease is due to an increased solution of gases in the blood and sudden liberation of them. The amount of gas capable of being dissolved by a liquid is, as Dalton showed, proportional to pressure. This law holds good for the workman in the caisson. Since under the influence of compression more gas is dissolved in the blood, the excess has to be liberated during the act of decompression. If this is done quickly there is an escape of bubbles of gas from the blood as it circulates through the capillaries in the spinal cord and elsewhere. When Paul Bert, a French physiologist, exposed animals to the influence of compressed air and quickly decompressed them, several of them died suddenly, and at the autopsy free gas was found in the blood and in the right side of the heart. Other animals were paralysed, and in them bubbles of gas were found in the spinal cord, while the subcutaneous tissue was at places emphysematous or filled with air. As to the nature of the gas found in the blood and tissues it is impossible to speak with certainty. It is probably nitrogen, for this gas is the largest constituent of atmospheric air, and it is perfectly passive, so that any effect produced by it would be purely mechanical. If we regard caisson disease as due to the liberation of gases dissolved in the blood during too rapid decompression, we have an explanation of such a circumstance as that of workmen taking ill shortly after they emerge from the lock, also the benefit which they receive by being put back into the cylinder and of undergoing temporary recompression.

_Treatment._--Treatment is preventive and curative. The points that above all others demand attention are that the acts of compression and decompression should be very slowly accomplished. Of these two, decompression is the more important. The workman should not be too rapidly pushed through the lock or exposed to any sudden increment or decrement of pressure. One minute for every three pounds of pressure is regarded as the average period, but this length of time might with advantage be lengthened especially for decompression, since it is the more dangerous. At this time too the workman, although he does not feel fatigued, is perspiring freely, and he is exposed to chill owing to a falling temperature. The air inside the caisson should be kept as pure as possible, and the men ought not to work longer than from two to four hours at a stretch. Even the minimum stated here may require to be halved as greater depths are reached. Men should be medically selected for the work, and only healthy men chosen who are free from heart disease, pulmonary and nasal catarrh, and who are temperate. No man who is suffering from a discharge from the ear ought to be allowed into a caisson, for even in healthy men the drum of the ear has been known to become ruptured. There ought to be a warm shelter or cabin at hand in which the men could lie down after coming out of the cylinders, and where hot non-intoxicating drinks can be got if required. If the men on coming out of the caisson are cold and collapsed, warm bottles should be applied to their extremities, medical assistance sought, and if the breathing is impaired a hypodermic injection of liquor strychniæ should be administered. Stimulants should only be given if there is failure of the heart’s action. Subsequently, if there is severe muscular pain morphia may be required. In the view that the symptoms are due to congestion of the internal organs ergot has been recommended. When unpleasant and dangerous symptoms have occurred immediately the workman has emerged from the caisson, good results have been obtained by subjecting him to recompression. Part of the cabin or shelter just recommended might be so constructed that recompression could be carried out therein under careful supervision, with the workman in the recumbent position.

_Dangers Incidental to the Making of, and Working in, Tunnels._

The making of tunnels has been carried on from remote ages, there being records of such works as early as six hundred years before the Christian era. In a paper read by Mr Francis Fox, M.Inst. C.E., before the Royal Institution, 25th May 1900, the methods adopted for making tunnels are described at length, and especially the making of the great Alpine tunnels. The dangers of tunnelling the Alps have been considerable, and now that the act has been accomplished, there has been experienced considerable difficulty in ventilating some of the tunnels. The _Mont Cenis_ tunnel is 8 miles in length, and as there is a gradient of 1 in 40 on the French side for the first 7 kilometres,[157] the trains go through with the regulators of the engine full open, so that if the wind is blowing in the same direction, great volumes of smoke practically travel with the train. For the men who are working in the tunnel there are refuges placed at every kilometre. Here when the men shut themselves in they can obtain compressed air, fresh water, and medicines, and by means of the telephone, extending in both directions, they can make their wants known outside. The caretakers of the tunnel work in pairs, so that if one man is affected by want of oxygen or through the density of the smoke, the other can render assistance, or telephone for relief, or they can both retire into a refuge and wait for either the air of the tunnel to clear or for a locomotive to come and remove them.

The _St Gothard_ tunnel is 9.3 miles in length. It is on the railway from Lucerne to Chiaso on the Italian frontier. The north portal of the tunnel has an altitude of 3639 feet above the level of the sea, and the south portal 3757. Ten years were spent in tunnelling the mountain. The work was accomplished at a great sacrifice of human life. In constructing the tunnel there were 580 accidents, of which 177 were fatal. The engineer and contractor lost their lives. There was a great mortality, too, among the horses. This excessive loss of life was attributed to insufficient ventilation, high temperatures in the tunnel, exposure of the men to the rigours of an Alpine climate after leaving their work, carelessness of the men in not changing their wet clothes, the poor character of the food supplied to the men, and defective sanitary arrangements. One of the great difficulties as regards the St Gothard tunnel has been its ventilation. The height of the mountain prevented the sinking of a shaft, but a large ventilating fan placed near the mouth of the tunnel blows air through the annular space between the arch of the tunnel and the gauge of maximum construction, whereby 210,000 cubic feet of air are thrown into the tunnel every minute, or 100 cubic metres per second. Before the fan was brought into operation the temperature used sometimes to be as high as 107° F., with 97 per cent. of moisture, but by artificial ventilation the temperature fell to 81° F., subsequently to 74.5° F. The tunnel can now be kept cool and comparatively free from smoke and vapour. Formerly the engine drivers and passengers were seriously indisposed in going through the tunnel; to-day they can travel without any inconvenience. In the St Gothard tunnel the amount of carbonic acid often exceeded 15 per 1000. There resulted from this and other causes such a corrosion of the rails, that it was necessary at the end of every few years to entirely replace the rails and their connections. The engineers estimated that during three and a half years each rail lost on an average 18 kilos in weight, and at a maximum 28 kilos. Similar metallic corrosion has been observed in the tunnel between Genoa and Turin, and is attributed to the sulphurous acid in the smoke of the coal becoming converted into sulphuric acid. The recent artificial ventilation of the St Gothard tunnel by the Saccardo system has not only made the air purer but increased the longevity of the permanent way.

The _Simplon_ tunnel is now in course of formation. In the first eighteen months three miles were made. When finished it will measure 12.26 miles between the north or Swiss portal on the Brigue side of the Alps and the south or Italian opening at Iselle. Such are the existing engineering and hygienic arrangements that they are believed likely to prevent the heavy death-rate that occurred in tunnelling the St Gothard. Fifty times the amount of atmospheric air is being sent into the tunnel than was forced into the St Gothard, and there are means in use whereby the air is cooled by jets of water. The great difficulty of the enterprise, as Professor Pagliani showed (_Revue d’Hygiene_, 20 Juin 1900), lies in keeping the temperature low and in renewing the air, so that the work of excavation and construction can be conveniently carried on without undue fatigue to the men. In the centre of the tunnel a temperature of from 107.6° F. to 113° F. is expected to be met with. The best possible means will be adopted to cool and ventilate the passages. The effect of high temperatures upon the men working in the tunnel is to increase the tension of carbonic acid in their blood and to interfere with respiratory exchanges. The moist atmosphere, too, tends to induce both pulmonary and circulatory troubles by preventing elimination of waste material through the perspiration. It is impossible for hard muscular work to be continued for any length of time, and to be efficacious in a temperature equal or superior to that of the human body, and in a close medium saturated with moisture. At 84° F. we know physiologically that muscular effort is considerably reduced. An attempt is being made to keep the temperature of the tunnel at 77° F., and lower when possible.

Two parallel galleries--in other words, two tunnels--are being run into the mountain 17 metres[158] apart, and are reunited by a small transverse gallery every 200 metres. As the entrance into the tunnel, on each side of the mountain, is on a curve, there is at either end a “gallery of direction” to correct errors of alignment direct from the two observatories in the axis of the tunnel. Pagliani found that the amount of carbonic acid at various distances varied from 0.68 to 7.53 per 1000, and the temperature from 75.2° F. to 87.8°, but these amounts vary with the activity of the ventilation, the number of men working, the activity of the machinery, and the moisture of the air, which is nearly always at the point of saturation. It is almost impossible to have a dry atmosphere; besides it is vitiated by the products of dynamite explosions.

The chief feature of the Simplon tunnel[159] “is the much lower altitude of the rails above sea-level than any of the other Alpine tunnels. This altitude is at its highest point 2314 feet, being 1474 feet lower level than that of the St Gothard, 1934 feet lower than that of the Mont Cenis....

“The tunnel enters the mountain at the present level of the railway at Brigue ... but on the Iselle side the connecting line with the existing railway at Domo d’Ossola necessitates heavy work.... The gradient on the northern portion of the tunnel will only be that sufficient for drainage, viz., 1 in 500, but on the southern portion the gradient will be 7 per 1000, or 1 in 142.”

FIG. 77.--Interior of Bath-house and Vestiary for the
Miners at the Simplon Tunnel (Iselle), showing the cubicles
provided with hot and cold water douche pipes, also numerous
cords with workmen’s apparel suspended from ceiling.]

In May 1901, I visited the Simplon tunnel, with the object of inspecting the methods of ventilation, the hospitals, the system of baths, and the houses erected for the working men, married and unmarried. Armed with letters of introduction from Mr Francis Fox, I was received at Iselle, the Italian side of the tunnel, by Mr Sulser-Ziegler, Director of Messrs Brandt, Brandau & Cie, Zurich; also by Dr Volante, the resident Medical Officer, who conducted me over the works, the workmen’s dwellings, and the hospital. From the elaborate precautions taken, it is clear that the Company has made up its mind not to repeat the errors of the St Gothard, and to show to the engineering world and the public generally that tunnel-making can be conducted without greater risk to life and health than occurs in any ordinary enterprise. The large number of deaths in the St Gothard was due to the imperfect system of ventilation, the difficulty of dealing with excessive temperatures in the mountain, and defective sanitary arrangements. Before operations at the Simplon were commenced, Mr Sulser and his colleagues appointed two medical men, one at either end of the proposed tunnel, viz., Dr Volante at Iselle and Dr Pommata at Brigue. Both are Italians, and are most capable men. Before undertaking work the men are all medically examined. By this means, only healthy men have been employed from the commencement. The most important problem has been that of ventilation. The Simplon tunnel, when completed, will be the longest in the world, being upwards of 12 miles in length. So satisfactory have the operations proceeded until now, that unless some untoward and unexpected event happens, the tunnel will be completed with the smallest number of deaths on record.[160] A short description of the work, based upon personal inspection, may well be added here.

Ventilation, as already stated, is the main difficulty. At the Swiss end of the mountain a shaft has been sunk into the tunnel, and up this the foul air is removed by wood fires. Into the tunnel, at each end, by means of large fans, air is introduced to the extent of 19 million cubic feet per day, or 13,200 cubic feet per minute. The air is carried in by one of the two parallel tunnels as far as the most recently constructed cross gallery, thence it is carried to the face by pipes. It returns by the larger tunnel, _i.e._, the one through which trains will ultimately travel. By this means fresh air is carried to the head of the tunnel where the men are working. At Iselle there are 500 men always at work in the tunnel. There are three shifts of men, and they work 8 hours each, so that 1500 men, roughly speaking, are employed at the Italian end, and a much larger number at Brigue. The average temperature at the head varies from 73° F. upwards. After firing with dynamite it may be as high as 80° F., or 86° F. The air is not only ladened with carbonic acid given off from the lungs of the men and the 15 to 20 horses in the tunnel, but contains materials given off from the bodies of the men during excessive perspiration, and is polluted by the products of dynamite and gelatine explosions. The foul air as it escapes from the mouth of the tunnel is thick and greyish-white in colour; it contains a good deal of smoke from the lamps of the workmen, and is very offensive. Small wonder, therefore, that the men emerge from the tunnel bathed in perspiration, and disposed to be chilled owing to their clothes being wet, for, although they work in tarpaulins, there is a good deal of water in the tunnel. It was, among other things, want of attention to these particular details in the St Gothard that caused so many deaths and illnesses from pulmonary disease.

Close to the mouth of the Simplon tunnel at Iselle, where the railway trucks draw up that bring the men from their work in the interior of the mountain, are large wooden buildings, one of which internally is divided off into, among other things, 32 cubicles, each of which is fitted up with hot and cold water pipes. The railway platform where the men emerge is covered over, so that the workmen can reach this building without being exposed to wet or cold. The building alluded to is not only a bath-house but a vestiary as well. Here the men in going to work in the tunnel put on their working clothes. At first sight, part of the interior of the bath-house is not unlike an old-clothes’ shop, for, on looking upwards, the clothes of the workmen can be seen suspended from the ceiling. There are 2000 strong cords placed 1 foot 6 inches apart. Attached to the free end of each cord are three iron hooks and a soap dish. Upon the hooks the workman hangs his clothes. As every cord is provided with a pulley and is numbered, each man, having had a bath after his day’s work, hangs his wet clothes on the hooks and draws them up to the ceiling. Next morning he finds his clothes ready for him, dry, warm, and comfortable. The bath-house is kept at a warm temperature, and is well ventilated. I was particularly struck with the excellent system of baths, the vestiary arrangements, and the cleanliness of the interior, and am of opinion that prevention of chilling of the workmen after coming out of the hot tunnel has had much to do with keeping them healthy, and has warded off pulmonary and bronchial disease. The supply of drinking water is good, and so far there has been during the three years no case of typhoid fever at Iselle. The workmen’s dwellings are also good, so, too, is the hospital and its administration.

In addition to the ill-health caused by working in the vitiated atmosphere and high temperature of the tunnels, the miners employed in making the St Gothard tunnel suffered from a peculiar form of anæmia, which for long was unexplained. The discovery of the cause of this “maladie des tunnels,” for so it came to be called, was made by Perroncito of Turin, who showed that the anæmia of the miners was caused by the presence of a parasite which fixes itself in the upper part of the small intestine, measures from ¼ to ½ an inch in length, and possesses a mouth and four long hooklets. By its hooklets the parasite fixes itself to the lining membrane of the human intestine, and is thus enabled to suck the blood of its host. The worm is called “Anchylostomum Duodenale,” and is known to be prevalent in Italy. It would appear, therefore, that the ova of this parasite escaping by the fæces of miners who are suffering from anchylostomiasis find in the heat and moisture of the tunnel a medium favourable for their transformation into the larval stage; while in the dirty habits of the miners, and the accidental contamination of their food and drink, lies the explanation of the means of ingress of the ova into the alimentary canal. Anchylostomiasis is not therefore necessarily a disease of tunnels.[161] It was simply introduced into the St Gothard by infected miners. The malady is endemic in Piedmont and Lombardy. Dubini of Milan found in one hundred autopsies made upon the peasantry of these districts, anchylostomiasis present in twenty bodies, so that the disease had been apparently introduced into the St Gothard by Italian workmen. The ravages caused by this parasite show the necessity for miners working in tunnels disinfecting their stools by such means, for example, as sulphuric acid. It is to the careful medical examination of the workmen by Drs Volante and Pommata, before being engaged by the firm, the elimination of all suspected persons, and the repeated inspection of the closets in the tunnel, that anchylostomiasis has not appeared at the Simplon. Since much of the pulmonary disease that affected the miners was consequent upon breathing an overheated and an excessively moist atmosphere, one also vitiated by the products of human respiration and dynamite explosions, improved ventilation in the case of the Simplon tunnel has diminished these evils; while the opportunities given to the men of changing their wet clothes, of bathing themselves, and of receiving shelter when tired, have prevented the acute bronchial and pulmonary catarrhs that were observed in making the other great Alpine tunnels.

_Underground Railways._

Of the underground railways in this country the only one I need allude to is the London Metropolitan. In 1897 a Board of Trade Commission was appointed to inquire into the condition of the air in the “Inner Circle” of the Metropolitan. The passenger traffic on this line is enormous. Between Praed Street and Aldgate stations, in one hour, as many as 38 trains were said to arrive and depart from either side of the stations. Welsh coal is consumed. Part of the Metropolitan railway is underground, and part is in the open, so that when the wind is blowing in certain directions passengers have been inconvenienced by the smoke and the insufficiency of the ventilation, despite the numerous escape holes. There has often been an excess of carbonic acid, sometimes, too, of carbon monoxide, in the air in the tunnels. The Commission found that the ventilation could not be adequately assured by the exchange and renewal of the air at the stations and the escape holes. It recognised the necessity for artificial ventilation, and in consequence the centrifugal method was adopted.

Vitiation of the air of a tunnel is caused by the gases that come from the means adopted for illuminating purposes, the products of respiration, and those due to combustion of coal in the furnace of the locomotive. Carbonic acid is only dangerous when it is present in large quantities. Breathed for a very short time at 60 per 1000 it causes headache, at 100 per 1000 respiration becomes extremely difficult, while if present in the proportion of 250 per 1000 it will cause rapid death.[162] It is seldom, however, that carbonic acid is even present to the extent of 10 per 1000; if present, it is as a rule accidental and only for a short period, so that danger from this gas is slight.

It is otherwise with carbon monoxide, a gas much more dangerous and subtle in its influence than carbon dioxide, popularly known as carbonic acid. Carbon monoxide was found to be present in the air of the Metropolitan Railway to the extent of 0.66 per 1000. When present to this amount in air it can, if time is given, paralyse the hæmoglobin or coloured substance of the blood that carries the oxygen to the tissues. Harmful effects can occur when carbon monoxide reaches 0.3 per 1000, but as it requires half-an-hour for the blood to absorb sufficient of this gas to be detrimental to the individual, accidents do not happen owing to the short length of the tunnels and the good speed of the trains through them. The risks to health are incurred mostly by the men who work on the railways. M. Raymond Godfernaux (_Génie Civil._, Août et Sept. 1899), in reviewing this subject, remarks that the breathing by an individual in repose for one and a half hours (less than this if work is being done) of an atmosphere containing 0.25 of carbon monoxide per 1000 is sufficient to cause unpleasant symptoms; if the air contains 0.5 per 1000 there will be debility and vertigo; if 0.9 per 1000 walking becomes impossible, while death will supervene if there is 1.5 in 1000. To men employed on underground railways, danger from this source only comes when the amount of carbon monoxide passes beyond 0.25 per 1000. The passengers run, practically speaking, no risk.

A heavy sulphurous odour hangs about the tunnels and stations of the Metropolitan Railway due to the combustion of coal. When sulphurous acid is present in air to the extent of 0.6 per 1000 it may cause death. This proportion is never present in the air of the tunnels of the Metropolitan of London.

The sulphurous acid and carbonic acid are believed to be proportional to each other. The amount of sulphurous acid is 440 times less than that of carbonic acid, and as the maximum of carbonic acid was 8.9 per 1000, sulphurous acid is seldom more than 0.02 per 1000.

The Commission established the facts (1) that there was a constant relation between the deleterious gases in the tunnels, and (2) that the proportion of carbonic acid present might be taken as the basis for the aeration of the tunnels. The proportion of carbon monoxide is constant, and corresponds to one-thirteenth the volume of carbon dioxide, while that of sulphurous acid is 440 times less than that of carbon dioxide. The amount of sulphurous acid is regulated by the character of the coal burnt in the locomotive. Some coals contain more sulphur than others. A similar remark applies to carbon monoxide. An Italian Commission charged with a similar function in regard to the composition of the air in the tunnels of its own country arrived at different chemical conclusions to the Commission of the Board of Trade, so that it would be scarcely wise to calculate the purity of the air in all tunnels upon parallel lines.

The amounts of carbon monoxide and dioxide should be estimated separately. The composition of the air of the tunnels of the Metropolitan, accepted for a maximum, is 1.5 of carbonic acid per 1000 (0.3 being regarded as the normal), 0.1 carbon monoxide per 1000, and 0.0027 sulphurous acid per 1000.

It is especially for the sake of the men who are working in the tunnels, and for the drivers of the locomotives, rather than for the passengers who spend proportionally a very short time on the railway, although of course desirable for all, that such artificial means of ventilation should exist as will quickly disperse the smoke and all combustion products.

It has been decided to introduce electric traction in the underground railway. By this means the Metropolitan Railway Company will rid the atmosphere in the tunnels of the impurities alluded to.

_Divers’ Paralysis._

Men when clad in proper diving suits and wearing air-tight head-gear can work at very considerable depths under water. At the depth of 33 feet the pressure is about twice that of the atmosphere. It is not exactly known to what depth men may descend with safety, but 201 feet have been reached, _i.e._, equivalent to a pressure of 87 lbs. to the square inch. It is very desirable that the descent should be made gradually, say about two feet per second. In this country diving is resorted to for making excavations connected with piers, inspecting sunken ships, etc., and abroad for sponge, pearl, and coral fishing. It is not uncommon for the men after having been in the water some time to complain of weakness of the legs and of impaired sensation. A patient of Dr Frederick Taylor (_Clin. Jour._, April 27, 1898), after diving 162 feet felt sick, and when pulled up into the lighter was found to have lost the power of his legs. Loss of consciousness is a frequent symptom, and as it often takes a man as much as five minutes before he can reach the surface of the water, there is considerable danger attending the occupation. Divers have died without regaining consciousness. Others when rescued, and on coming to themselves, have complained of severe cramp-like pains in the muscles of their limbs and abdomen.

At such depths as 160 to 180 feet men can only stay at the bottom of the sea a very short time. It is only when men work at very great depths that paralysis is likely to supervene. The risk to life and health is regulated by the depth, and particularly is this the case when there are sudden alterations of pressure. Hauling up divers too quickly when the air-tube has become foul is a very dangerous proceeding. Since young men bear the work better than old men, age, therefore, is a circumstance that should be considered, as well as temperance in the use of alcohol. The character of the water and the length of the period of submersion must not be overlooked. Once 150 feet below the surface has been reached, the diver is apt to feel somewhat inconvenienced, and with every increase of two or three feet beyond this, the inconvenience becomes rapidly greater. There are experienced a sense of fulness in the head, buzzing in the ears--often relieved by filling the mouth with saliva and swallowing the secretion--also flashes of light before the eyes. Bleeding at the nose, mouth, and ears occasionally occurs after the men come to the surface; severe muscular pains, called “bends,” are sometimes complained of, followed by loss of power in the legs. There is either complete paraplegia, _i.e._, the lower half of the body is paralysed as regards motion, and sometimes too as regards sensation, or the loss of power is limited to groups of muscles affecting the wrists and ankles. The paralysis may be permanent, or it may last only a few hours or days, but if a diver has once had paralysis the symptoms are apt to recur on re-exposure.

The cause of divers’ paralysis, like the disease of caisson workers, is the sudden liberation of gas that was previously dissolved in the blood. No hæmorrhages have been found in the central nervous system, but Van Leyden observed fissures in the spinal cord occupied by leucocytes, _i.e._, cells like the white corpuscles of the blood. The appearance of the fissures suggested that they had first been formed, and that the colourless corpuscles had found their way thither afterwards. When lesions have been present in the spinal cord they usually occupy the lowest third of its length, a circumstance attributed by Moxon to the greater length, tortuosity, and attenuated condition of the small blood-vessels that are present at this particular part compared with the arteries in the upper region of the spinal cord.

Fatal cases of divers’ paralysis fortunately do not occur very frequently. One of the most recent cases was in November 1900, when H.M. battleship _Howe_ was cruising in the West of Scotland; the diver of the ship died after a lengthened immersion in the water. At the post-mortem examination bubbles of gas were found in the blood-vessels, the heart, and brain. The morbid conditions found in this man’s body after death quite confirm the opinion already expressed as to the pathology of the malady.

In addition to the risks to health already mentioned, there are those incidental to the fouling of the air-tubes of the diver; also large stones and other materials occasionally fall upon the tubes, and tend to cause death by asphyxia.

So far as the operations of diving itself are concerned the three things to be avoided are: (1) too great depths; (2) sudden alteration of pressure; and (3) coming up too suddenly. There must necessarily be increased danger when a man who is working at a depth of 150 feet is brought to the surface in one minute instead of five.

_Treatment._--If the diver on coming to the surface is found to be unconscious and not breathing well, artificial respiration should be resorted to and kept up till breathing becomes automatic. If he is collapsed, warmth should be applied to the extremities, and, if he can swallow, hot coffee should be administered. The patient should be removed to a hospital, or his own home, when sufficiently revived. If muscular pains are severe, or if there is loss of power, rest in bed, sinapisms to the spine, and later on galvanism should be tried.

THOMAS OLIVER.