« PředchozíPokračovat »
The disease of silicosis has been defined to you already, I believe, as a disease due to breathing air containing silica dust.
It is a disease due to breathing air containing silica, characterized anatomically by generalized fibrotic changes and the development of miliary nodulation in both lungs, and clinically, by shortness of breath, decreased chest expansion, lessened capacity for work, absence of fever, increased susceptibility to tuberculosis—some or all of which symptoms may be present—and by characteristic X-ray findings. There is a nodular formation throughout the lung fields. That is determined by X-ray findings.
Silicosis is not a new disease. Collis gives a very complete report on the literature from the time of Hippocrates up to the present time. Hippocrates spoke of the metal figure of a man who breathed with difficulty and had other symptoms similar to those found in silicosis.
Agricola, in 1557, stated that:
Some mines are very dry, and the constant dust enters the blood and lungs, producing the difficulty of breathing the Greeks call asthma. When the dust is corrosive, it ulcerates the lungs and produces consumption, hence it is that in the Carpathian Mountains there are women who have married seven husbands, all of whom this dreadful disease has brought to an early grave.
Lohneiss, in 1690, referring to miners, describes the effects on them as follows:
The dust and stone fall upon the lungs, the men have lung disease, breathe with difficulty, and at last take consumption.
In 1713 a British patent was granted for grinding flint by wet methods. Previously the flint were pounded dry which
Proved very destructive to mankind, so much that any person, ever so healthful and strong, working in that business cannot possibly survive over 2 years, occasioned by the dust sucked into his body by the air he breathes.
In 1862 Dr. Peacock gave a report based on an examination of more than 600 miners, in which he established the existence of miners' disease, distinguishing it from true phthisis, stating that,
The quickness of pulse, the rapid and extreme emaciation, and the high perspiration so characteristic of true phthisis are generally absent or only slightly marked.
In 1902 a committee, of which Dr. J. S. Haldane was a member, reinvestigated the causation of the phthisis mortality among Cornish tin miners, and decided that,
So far as the Cornish miners are concerned, it seems evident enough that stone dust, which they inhale, produces permanent injury to the lung, gradually in the case of ordinary miners, and rapidly in the case of machine drill
That the primary injury to the lung is due solely to the inhalation of dust would seem to be practically certain.
In 1905 the western Australian commission on ventilation and sanitation of mines made reference to miners' phthisis, and in 1907 a report on miners' phthisis at Bendigo was issued by Dr. W. Summons. In 1910 Dr. J. H. L. Cumpston reported on his study among the miners in western Australia. In 1909 pneumoconiosis was scheduled as an accident under the workmen's compensation act in New Zealand, but that was repealed by the end of that year.
Mr. RANDOLPH. Why was it repealed ?
Dr. SAYERS. I do not know why it was repealed, but apparently it was hard to apply at that time. I may say that they now have such a law.
In 1910 the national conference held in Chicago called attention to an interstitial pneumonia which prevailed in some of the lead and zinc mines of Missouri and in deep mines of Utah and Nevada. Although the disease was known before 1899 in the Transvaal, it was not until 1902 that a commission was appointed there to inquire into the extent that the disease prevailed there. In 1911 a sanitorium was opened for the accommodation of patients, and in that same year a miners' phthisis commission was appointed, which issued a report dealing rather fully with miners' phthisis among white miners.
Officers of the United States Public Health Service have visited these various countries, Australia, New Zealand, South Africa, Europe, and 17 countries were represented in 1934 when this subject was discussed at Geneva.
There is literature from 26 countries abstracted on this subject in a recent bibliography.
Silicosis is present in many of the mining districts of the United States. In 1914 Dr. A. J. Lanza found that 433 miners of 720 examined in the Joplin, Mo., district had silicosis.
He also found in 1916 that 432 of 1,018 examined in Butte, Mont., were so affected. Those studies were made in conjunction with the Bureau of Mines, I might add. There has been no time since then that the Public Health Service has not been associated with the study of this disease in the United States.
In 1922 Jarvis and Hoffman found the mortality from this disease to be very high among granite workers in the State of Vermont. In 1929 Dr. A. E. Russell and others, of the United States Public Health Service, completed a study in this same district, in which study they found the universal occurrence of silicosis among the workers, but an absence of death from silicosis per se, tuberculosis apparently always intervening.
An investigation was made in 1926 by Hayhurst and his coworkers in one of the largest and deepest sandstone districts in the world, located in Ohio, and worked for more than 50 years. The workmen were employed by two quarry companies which marketed grindstones, scythestones, curbing, flagging, breakwater, and building stones, and also furnace sand. The investigators state that of 260 men having silicosis only 13, or 6 percent, had tuberculosis, as compared with the 20 to 30 percent reported as usually found present by silicosis studies throughout the world. No explanation can be found yet for this anomaly.
In 1932 the mining companies of the tri-State district of Kansas, Missouri, and Oklahoma, in the interest of the health and safety of their employees, requested the Bureau of Mines to determine whether measures in use for the prevention of silicosis were adequate, and, if not, to recommend improvements. This investigation included the examination of 309 miners, of whom 101 were found to be negative, 114 doubtful, and 94 positive for silicosis.
In 1924 a small clinic with a physician and a clerk on duty was organized at Picher, Okla., to conduct examination of miners. In 1926 more men were applying for examination than the small force at the clinic could handle. In 1927 the Metropolitan Life Insurance Co. and the mine operators through their association entered into an agreement with the United States Department of Commerce, through the Bureau of Mines, to supply additional funds to expand the work of the clinic in the Picher field. Investigation was completed on June 30, 1932, and the clinic turned over to the association for continuance. During the period covered by the Bureau's investigation, 27,553 miners and a number of women and children were examined. Five manuscripts, one for each year that the Picher clinic had been in operation, have been completed, and summarizing the first 2 years' work published. Of 7,722 miners and men seeking mine employment who were examined the first year of clinic operation, 5,704 were classified as negative, 1,362 as having first-stage silicosis, 253 as having second stage, 32 as having third stage, 267 were diagnosed as having silicosis complicated with tuberculosis, and 104 as having tuberculosis without silicosis.
We have carried on studies in Vermont, Pennsylvania, North Carolina, Georgia, and a number of other States. Altogether there are more than 30 States in which the disease occurs.
It is quite widespread.
Mr. Dunn of Pennsylvania. You mean the disease silicosis? Dr. SAYERS. Yes.
Mr. RANDOLPH. How many States have laws making silicosis compensable?
Dr. SAYERS. I believe there are only eight.
In 1929 a committee was appointed by the Industrial Commissioner of New York State to draft for recommendation to the Industrial Board rules relating to the regulation of rock drilling, sandblasting, and rock crushing. The same year an examination was made in New York City of 208 men exposed to rock dust in subway or tunnel construction. That is published by A. R. Smith. Silicosis was found to be present in 118, or 57 percent, of the men examined.
Silicosis probably occurs in the mining and allied industries throughout the world. Eight countries were represented at the international conference held in Johannesburg in 1930. A recent bibliography on pneumoconiosis lists references to the literature of 26 countries, as I have suggested. The disease occurs in the potteries, foundries, sand blasting, abrasive, granite, tool and ax grinding, glass, plate, silica grinding, and mining industries.
Since the literature of practically all the principal nations of the world contains articles on this subject, it is apparent that no nationality is exempt, and that all races are susceptible as shown by the wide distribution of silicosis. Although the incidence is higher among the younger miners in districts where the precentage of free silica is high, and among older miners where the percentage of silica is low, is in itself probably no great factor.
Previous occupation of the men may have a definite influence to silicosis, if they have been exposed to dust or to other respiratory irritants. According to some investigators, animal experiments indicate that coal dust has this effect. Three groups of animals were exposed for a definite time as follows. Group 1 to free silica dust,
group 2 to a mixture of coal dust and silica dust, and group 3 first to coal dust and then to silica dust. They were examined several months after exposure, and groups 1 and 2 had more silica remaining in the lungs than group 3, although silica dust could be demonstrated in all groups.
Men who have or have had respiratory diseases, especially tuberculosis, are apparently more readily affected by silica dust.
Silicosis has been divided arbitrarily into various stages. In South Africa the stages are defined in law as antiprimary, primary, and secondary. This same classification is followed also in Ontario. In the United States the stages are called first, second, and third. The committee on pneumoconiosis, referred to before, describes the stages as follows:
The first stage, corresponding to antiprimary stage of South Africa. The symptoms of uncomplicated first-stage silicosis are few and often indefinite. The man may apparently be quite well and his working capacity not noticeably impaired. Slight shortness of breath on exertion and some unproductive cough, often with recurrent colds, are the most usual symptoms. The man may have a little less ability to expand his chest than formerly, and the elasticity of the chest may be slightly impaired. The earliest specific indication of the presence of silicosis is the radiographic appearance, consisting of generalized arborization throughout both lung fields with more or less small, discrete mottling.
This characteristic mottling is due to shadows cast by the discrete individual nodules of fibrosis tissue in the lungs and is essential to the diagnosis of silicosis. Without this finding the diagnosis of silicosis is not sustained except by autopsy.
The second stage, corresponding to the primary stage of South Africa. A definite shortness of breath on exertion is usually found, and pains in the chest are a frequent complaint. A dry morning cough is often present, sometimes with vomiting, and recurrent colds are more frequent. Even then, the man's appearance may be healthy, but he is dyspnoeic on exertion, he cannot work as well as formerly, his chest expansion is noticeably decreased, the movement being sluggish and diminished in elasticity.
The characteristic radiographic appearance is a generalized, medium-sized mottling throughout both lung fields. The shadows of the individual nodules are for the most part discrete and well-defined on a background of fiber arborization, but there may be here and there larger but limited opacities, due to irregular pleural thickening or to a localized aggregation of nodules.
Third stage, corresponding to the secondary stage of South Africa. In the third stage the shortness of breath is marked and distressing even on slight exertion. The cough is more frequent; the expectoration is in most cases slight, but may be copious. The individual's capacity for work becomes seriously and permanently impaired; his expansion is greatly decreased, even with forced inspiration; he may lose flesh; his pulse rate may be increased, and his heart may become dilated.
The radiographic appearances in the first stage are further accentuated, the mottling is more intense, the nodules are larger and take on a conglomerate form so that large shadows are shown corresponding to areas of dense fibrosis.
Physical examination of an individual may reveal changes in percussion and ausculation, mild in the first stage and increasing with the progress of the disease. These alone are not sufficient to be of great value in the diagnosis of silicosis.
The pathology of psychosis is well summarized in the statement on the medical aspects of silicosis made at the international conference on silicosis held in Johannesburg, August 13 to 27, 1930. It was agreed that the microscopic pathological changes that may be produced by the prolonged inhalation of silica dust are as follows:
(a) The development of a condition designated in South Africa as a dry bronchiolitis, characterized by an accumulation of dust-filled phagocytes in or in relation to the terminal bronchioles, with possibly some desquamation of their epithelium.
(6) The accumulation of dust-containing phagocytes about and in the interpulmonary lymphoid tissue, and their transportation through the lymphatics into the tracheobronchial lymph nodes. (The conditions described under (a) and (b) do not constitute the disease silicosis.)
(c) The gradual development of fibrous tissue within such accumulation of phagocytes and the formation of characteristic nodules of hyaline fibrous tissue.
(d) Degenerative changes in these poci.
(e) The hyaline nodules increase in size by extension at their periphery. Coalescence of adjacent nodules takes place and brings about involvement of further areas of the lung. (The conditions described under (c), (d), and (e) constitute the disease silicosis.)
Dr. Watkins Pitchford calls attention to the fact that, due to the effect of the silica that remains in the lungs, the disease may progress for some time after the individual is no longer exposed to breathing the silicuous dust. However, a man suffering from simple silicosis may improve when removed from the dust atmosphere and placed in suitable surroundings.
Recovery does not mean restoration of the tissue in the lungs to normal but subsidence of the inflammatory changes and symptoms. Susceptibility to infection is increased in all stages of silicosis, but infection is more frequent in the latter stages and contributes largely to the severity and progress of the disease. When any worker who has silicosis develops a cold of more than 3 days' duration, he should be thoroughly examined and treated by a physician to arrest the disease at once.
If breathing a dust causes a disease, evidently the disease would not result if the dust were not in the air breathed. In order to control the dustiness of the air, the amount of dust present must be determined. Two factors are usually considered, namely, the weight and the number of particles in a given quantity of air. Many instruments have been devised for making these determinations, but any instrument to be of value must be able to remove a large percentage of the dust from the sample of air and retain it in a form that may be examined. The sugar-tube method and the konimeter were used in South Africa and later in other parts of the world, including the United States. More recently the impinger, developed by Leonard Greenburg, of the United States Public Health Service, and G. W. Smith, of the United States Bureau of Mines, has been the method of choice in the United States. Among some of the other instruments are the Read water spray dust collector, the Kotze hydrokonimeter, of South Africa, the Owen dust counter, and the electric dust collector of Philip Drinker.
The instruments mentioned will give information as to the condition of the air but will not aid in any way in protecting the men breathing it. The men will be protected, first, if no dust is formed; secondly, if, when formed, the dust is prevented from getting into the air; thirdly, if once in the air the dust is removed from the air; and, fourthly, if the dusty air is replaced by clean air.
In the mining industry, wet methods have been used to prevent the dust from getting into the air to be breathed, as wet drilling, wetting the working face and the rock or bore before shoveling. This method has materially reduced the number of cases of silicosis produced.
In the tool- and ax-grinding industry, wet methods were found to be less efficacious than dry exhaust. Recently exhaust systems