A natural history of spirometry

The invention of a measurement proxy for lung capacity – that is, vital capacity – can be contextualized as part of a wider scientific programme to statistically analyse the norms of human bodies through instrument-based measurements. Scholars have traced the start of both large-scale statistical studies and anthropometric measurements to the late nineteenth century, in which statistics about the human body gained authority in an increasingly eugenic framework.Footnote ¹² Within this framework, the concept of disability emerged to categorize aberration from the norm.Footnote ¹³ Categorization was a crucial force in promoting the definition and standardization of disability. As sociologist Matthew Kohrman explains, the rise of statistics prompted both a greater awareness and a standardization of disability.Footnote ¹⁴

Vital capacity gained medical credence in this statistical milieu primarily through the effort of John Hutchinson and his 1842 spirometer. Spirometers’ accurate ability to predict premature mortality led Hutchinson to suggest that they should be used in actuarial prediction for life insurance policies.Footnote ¹⁵ Similar devices, known as pulmometers, had been used previously in clinical investigations, for example by Charles Turner Thackrah (1795–1833) in his 1832 study of the industrial workers of Leeds.Footnote ¹⁶ However, Hutchinson is regarded as the inventor of vital capacity because he found that with every inch of height vital capacity increased by eight cubic inches.Footnote ¹⁷ He arrived at this conclusion after using the spirometer to collect data from over four thousand test subjects, categorized by variables including occupation and class. He divided his subjects into types, including paupers, sailors, firemen, grenadier guards, mixed classes, diseased cases, gentlemen and pugilists.Footnote ¹⁸ Hutchinson then created correspondent tables showing what the ideal vital capacity ought to be for height. The spirometer thus presented vital capacity as lung capacity. As medical historian Lundy Braun argues, ‘with the help of this new, refined instrument, “lung capacity” became a discrete entity that could be measured, quantified, and ranked’.Footnote ¹⁹

However, attempts to accurately measure and scale breathing through the spirometer were complicated by the need to first define the measure for normal breathing – there can be no abnormal without an initial definition for the normal. Recurring questions over whether the parameters of normal breathing were universal or varied between groups marked all such attempts: normal breathing for whom? The classification and categorization of relevant group varieties perpetuated scientific acceptance of difference between these groups, and the notion that these groups constituted distinct natural kinds.Footnote ²⁰ This has been illuminated by Braun, who has identified that the practice of correcting for race in spirometry promoted scientific acceptance of difference between racial groups, without due concern for the racial categories employed to organize these data in the first place, or for the ways in which social conditions and living conditions affect lung function.Footnote ²¹ The classification of entities such as race, sex, disease and disability is highly controversial, and important, as in the process of being constructed they are often fashioned as natural divisions. As scholars such as Bowker and Star have attested, this is not so much a reflection of reality as a shaping of reality.Footnote ²² Yet the objectivity and trust that we associate with numbers mean that their related classification schema become invisible as their categories are replicated as though they are inevitable and natural – a process that philosopher Ian Hacking has described as ‘kind making’.Footnote ²³ The attempt to standardize the parameters of normal breathing has been complicated by the drive to categorize the social groups that should represent the standard of normal breathing for that particular group.

Hutchinson's ideal vital capacity tables represented the standard data sets for assessing normal lung function until the First World War, when Georges Dreyer asserted in 1919 that lung capacity standards for pilots needed to be more strictly measured.Footnote ²⁴ Vital capacity offered a quick and easy way to assess physical fitness and so was used routinely in the examination of candidates for the Royal Flying Corps, with the results leading to either rejection or acceptance based on an arbitrary minimum standard. Men with superior respiratory capabilities were sought out for their capacity to withstand the atmosphere of the open cockpits.Footnote ²⁵ Dreyer argued that Hutchinson's results did not give enough credence to the impact of weight on lung capacity and he created new data tables.Footnote ²⁶ In collaboration with the MRC he published The Assessment of Physical Fitness by Correlation of Vital Capacity and Certain Measurements of the Body in 1920 and dedicated the book to John Hutchinson. This was a large volume, comprising primarily hundreds of tables indicating the normal ranges for weight and height, and their correlation with vital capacity. It was clearly created as part of an effort to improve national fitness, with the military particularly in mind.

Dreyer was thus concerned more with improving fitness than with defining illness and he started the book with the assertion that the First World War had made physical fitness an issue of national importance. Moreover, he prophesied that ‘it is only when the meaning of “the normal” with respect to these measurements is understood, and when the limits of the normal have been properly defined, that it will be possible to study with any prospect of accuracy or success the deviations from the normal’.Footnote ²⁷ Dreyer categorized his results by grouping people into three classes – A, B and C – which represented the conditions of perfect, medium and poor physical fitness. These groupings corresponded closely with social class, with boys in public school placed in class A against children in upper-class schools who were categorized as class B. However, social class could be offset by certain occupational training, and so army and navy personnel and blacksmiths were placed in class A while upper-class clerks remained in class B. Using this system, the person being measured would first be placed into their appropriate division, and then their vital capacity percentage ascertained for their group.Footnote ²⁸ This allowed for the comparison of the relevant reference groups: age, sex, class and occupation.Footnote ²⁹ If the person was found to have

As Smith and Horrocks have argued, Dreyer's standardized method for classifying individuals’ health was particularly appealing to the Medical Research Council because of its emphasis on standardized laboratory medicine, and its lack of reliance on a clinician's subjective opinion.Footnote ³¹

In 1920, Wing Commander Martin Flack argued that the vital-capacity value could not adequately describe what was normal for any one individual and proposed the addition of a breath-holding test, which he believed could assess psychological fortitude as well as giving evidence of the healthy lungs needed for flying.Footnote ³² It is likely that this psychological addition was designed to identify applicants at risk of developing shell shock, which was of increasing public concern at that time, as well as working to mitigate the fear of malingering. The potential for malingerers to abuse the spirometry test by failing to cooperate was noted as a key concern in many studies using spirometry during this period.Footnote ³³ Moreover, miners who complained of breathlessness were often dismissed as malingerers, or their respiratory trouble was diagnosed as being of psychological origin.Footnote ³⁴

By the 1920s, Dreyer's standards had been largely discredited.Footnote ³⁵ In 1932, Dr Alan Moncrieff asserted that a more straightforward means of assessment was needed and pointed out (quite correctly) that the literature was strewn with disregarded methods and standards. Although he described breathlessness as ‘essentially a subjective phenomenon’, he felt that quantitative measures were necessary for evaluating the success of cardiovascular surgery and silicosis disability: ‘The advantage of such methods is that they provide a numerical statement of the degree of respiratory efficiency or failure, but the grave disadvantage is present for all of them that normal figures may provide a too rigid standard, and wide deviation may be possible in health’.Footnote ³⁶ New tests were needed.

This was especially urgent because of the increasing concern that mining workers were suffering from respiratory disability due to their exposure to coal dust. However, medical classifications, healthcare assessments and disability categorizations were connected and complicated by concerns regarding compensation. Attempts to reduce this complexity by the bureaucracies concerned with compensation were marked by attempts to use standardized objective measurements of disability. For example, the first comprehensive classification of disability in Britain was designed by the Ministry of Pensions in 1917 to provide pensions for the soldiers returning from the First World War with injuries.Footnote ³⁷ Compensation was provided in percentage degrees and this scaling was largely based on the visibility of the injury, a quality which historian Julie Anderson describes as critical to ‘the hierarchy of disablement’.Footnote ³⁸ She relates this concept to how disability pensions were scaled and calculated in accordance with the perceived usefulness of the disabled body for work.Footnote ³⁹ For example, despite some contemporary protest, deafened ex-servicemen were awarded not quite half of the full pension amount accorded to servicemen who had been blinded, based on the greater ability of the deafened man to work.Footnote ⁴⁰ Similarly, historian Heather Perry has demonstrated that in Germany during the First World War, prosthetics were designed to replace the functionality rather than the form of the missing limb.Footnote ⁴¹ Prosthetic arms were designed not to mimic the look and use of the lost limb, but to make the arm as useful and efficient as possible in the relevant work sphere.Footnote ⁴² Assessment for the compensation of disability has long been associated with the ability to work rather than the testimony of the patient, partly because this allowed for clear standards for compensation.

The ‘will to standardize’ in order to attain objectivity has been strong within the MRC and has been remarked upon by historians researching its standardization of audiometry, depression and Alzheimer's assessment guidelines.Footnote ⁴³ Far from being unproblematic and objective, the categorization of disease and disability in relation to statistics, standards and measurement thresholds is firmly embedded in a politico-social context. Indeed, the diverse national medical positions on the aetiology of silicosis have been shown to have been directly linked to the social insurance systems present in each different country.Footnote ⁴⁴ Measurement instruments are crucial in promoting standards that allow for easy replication, and easy comparison across different disciplines and locations. Standards are especially powerful because they self-perpetuate and, as Timmermans and Berg have demonstrated, standards can function as political tools. They explain that ‘standards are inherently political because their construction and application transform the practices in which they become embedded’.Footnote ⁴⁵ Historians of technology have long emphasized the fact that technical standards underwrite their own opacity and through doing so become increasingly invisible.Footnote ⁴⁶ Standards create conformations of both instruments and people. Such conformations have often been used to objectify and enforce group differences while at the same time perpetuating their invisibility.Footnote ⁴⁷ These constructions are then reified as though they represent objective measurement. As J.C. Gilson and P. Hugh-Jones reflected in their Medical Research Council special report, ‘we must be able to measure breathlessness, either by attempting a quantitative estimate of the symptom … or by arbitrarily selecting a particular physiological test as the best index and relating other test results to this standard’.Footnote ⁴⁸ We need to question the extent to which measurements can tell us something ‘real or true’ about the human body in cases when easily quantifiable measurements are artificially privileged in this way.Footnote ⁴⁹ The fight for recognition and compensation of ‘miner's lung’ is a clear example of the way in which politics and objective standards can conflict with testimony.

The Medical Research Council intervenes

Such testimony was provided in 1923 by a miner who wrote to the Somerset Miners’ Association's agent to question the compensation available for his illness. He wrote,

The miner's reference to the strength needed to fight the condition reflects the insights garnered by the Life of Breath Project principal investigators Carel and Macnaughton, who have explained that the psychological experience of breathlessness has an important effect on the personal perception of respiratory illness.Footnote ⁵⁰ This assessment has been reinforced by recent neuroimaging studies which have identified how variable psychological workings affect the way people experience the bodily sensation of breathlessness.Footnote ⁵¹ The strength that the miner believes he has means that he feels he can battle his illness from a better position than the older man. In the same letter he gives more details about the progressive nature of his disability:

The miner's assertion that X-rays ‘don't tell lies’ not only demonstrates faith in the apparently objective physical image, but also pre-emptively responds to potential accusations of malingering that constantly dogged the miner's claims of ill health. As his illness progressed without compensation he kept writing, describing his symptoms on one occasion by saying, ‘I have not breath enough to blow a candle out’.Footnote ⁵³ The writer was not diagnosed as suffering from silicosis until 1929, and he collapsed and died in July 1930, at the age of forty-five.Footnote ⁵⁴ Historian Joseph Melling has identified that his inquest was pivotal in motivating the subsequent legislative and scientific debates about pulmonary illness in the 1930s.Footnote ⁵⁵

Moreover, from the miner's letter we can see that the use of historically situated and highly specific metaphors supports the claim that a contextual understanding of breathlessness is vital.Footnote ⁵⁶ Oxley and Macnaughton have demonstrated that the language we use to demonstrate breathlessness is highly variable, and subject to difference between cultures and contexts.Footnote ⁵⁷ This is also true of the subjective and invisible experience of pain, which Joanna Bourke has recently examined through the metaphors that differ between times, genders, ethnicities and religion.Footnote ⁵⁸ She explains that ‘[s]ocial environments and physiology map themselves strongly in the figurative language people employ to communicate their pain’.Footnote ⁵⁹ While instrumentation is ideally designed to transcend such sociocultural contexts, the following section will demonstrate that the clinical investigation of respiratory disease in mining communities was impacted by the normalization of disability within these communities.

That pulmonary disease disproportionately affects mineworkers has been recognized from the early nineteenth century. However, by the end of that century, the orthodox medical position held that tuberculosis due to overcrowding was more likely to be the cause of miners’ respiratory distress than the levels of dust.Footnote ⁶⁰ Historian Michael Bloor has attributed the resultant shift in attention from dust in the air to germs in the air to developments in bacteriology.Footnote ⁶¹ Melling has added that subsequent commitment to this stance was partially fuelled by medics’ reluctance to be associated with old-fashioned Victorian fears about coal dust.Footnote ⁶² Moreover, following the work of J.S. Haldane, there was some adherence to the notion that coal dust functioned as a prophylactic. That is, coal dust was beneficial: ‘a little dust was good for you’.Footnote ⁶³ Indeed, D.C. Davies, who worked in Ffaldau colliery in 1930, described inhalation of coal dust being used in Llandough Hospital in the late 1930s as a treatment for silicosis.Footnote ⁶⁴ Notable amongst adherents to this view were the Home Office's medical factory inspector Dr Edgar Collis and the 1927 medical inspector of mines Dr Sydney Fisher, both of whom have been identified by Perchard and Gildart as key ‘merchant[s] of doubt’.Footnote ⁶⁵

In what follows, I set out a brief outline of the legislative changes relating to coal mining which preceded the MRC investigation. These changes were variously resisted or advocated by a number of important bodies, including the coal owners (represented by the Mining Association of Great Britain), the South Wales Mining Federation and other trade unions, medical specialists, the Home Office, the Mines Department, the Medical Research Council and the labouring communities. Historians disagree about which of these bodies were responsible for the ‘stuttering’ advances in occupational legislation, although there is consensus that complex social, cultural, economic and political forces interrelated with the contested aetiology of miner's lung.Footnote ⁶⁶

Compensation for industrial disease was first offered to industrial workers in 1906 through the UK Workmen's Compensation Act, although its extension had been strongly resisted by coal owners.Footnote ⁶⁷ This in turn followed a domestic government investigation into occupational disease, which resulted in diseases being added alongside injuries as eligible for compensation for the first time.Footnote ⁶⁸ This was despite the fact, as Bufton and Melling have noted, that the Home Office remained adamant throughout the interwar years that the state would not provide any funding for industrial compensation.Footnote ⁶⁹ Silicosis-specific compensation (for those exposed to silica dust) was introduced in 1918 but was only for quarrymen and workmen in other silica-based industries – it specifically excluded coal miners.Footnote ⁷⁰ The situation for coal miners improved marginally in 1929 thanks to the Various Industries (Silicosis) Scheme of 1928, but this scheme had strict eligibility criteria and only cases of death or of total disability that precluded future work were compensated.Footnote ⁷¹ The reasons for this were largely due to the difficulty of assessing partial disability, and also of diagnosing silicosis or pneumoconiosis in its early stage as a disease distinct from tuberculosis.Footnote ⁷² For the medico-legal bureaucracies involved with miners’ compensation, this meant that while the presence of illness was not disputed, the causation was highly contested.

In 1930 the Medical Research Council Committee on Industrial Pulmonary Disease was appointed, and in 1931 the Various Industries Scheme was extended to cover more workers and include partial disability.Footnote ⁷³ This may have been precipitated by Britain's substantial involvement in the 1930 International Labour Office Conference on silicosis in Johannesburg. Although the global transfer of silicosis knowledge was important in the development of consensus on mining-disease aetiology, historian Arthur McIvor has argued that the conference policies were unsuccessful in practically improving the situation for disabled workers with respiratory disease in Britain.Footnote ⁷⁴ These disabled workers had to obtain medical certificates from their own doctors before applying to the Medical Board, where their cases were usually presented by their trade union as the financial cost for individuals applying directly to the board was prohibitively high.Footnote ⁷⁵ The introduction of partial disability posed new challenges to the medical community in their ability to accurately and convincingly assess its boundaries and Braun argues that this was due to ‘the lack of correlation between the degree of tissue damage and the severity of breathlessness’.Footnote ⁷⁶ Assessing breathlessness as a symptom of disability was especially difficult and presented further challenges because of the need to correlate reported breathlessness to X-ray images. For instance, the MRC noted that symptoms of respiratory disability manifesting as coughs and breathlessness generally ran in parallel with X-ray changes but often could not be connected to any clinical evidence.Footnote ⁷⁷

Notwithstanding the condition of their lungs, if miners could not prove that they had been exposed to silica dust from working on rock containing at least 50 per cent silica, then their case could be overturned. Bufton and Melling have argued that this resulted in the prioritization of geological expertise over clinical criteria.Footnote ⁷⁸ This stipulation also reinforces the central claim of this paper, that socially useful numbers were crucial in negotiating the boundaries of contested disability and compensation. The subsequent lack of concordance between geological and pathological measures was reflected in the realization that ‘the relationship between geological conditions and the onset of disease could not be precisely measured’.Footnote ⁷⁹

For example, in the seminal 1935 appeal case of Wragg v. Samuel Fox & Co. Ltd (Sheffield), the county judge ruled,

Despite this seemingly damning testimony, when employers Samuel Fox & Co. appealed the decision, Lord Justice Greer took their side, because of the proviso in the Act which stated that the employer should not be liable if they could prove that the employee was not exposed to the silica rock.Footnote ⁸¹ The ability to do this rested on the applicant having the means to secure (expensive) expert testimony from geologists to back their claim and such support was sought by both the miners’ unions and the coal owners.Footnote ⁸² The Wragg v. Fox case proved to be pivotal in delaying any practical implementation of the 1931 scheme and influenced miners’ leaders in their lobbying for clear diagnostic criteria.Footnote ⁸³ The Various Industries (Silicosis) Scheme was thus amended in 1934 to extend to miners working underground, but partial disability would only be granted if ‘the nodular features of silica dust were detected on microscopy and X-ray’.Footnote ⁸⁴

Although both local doctors and miners were convinced of the existence of a disease due to coal dust, this belief did not correlate with diagnostic criteria for compensation.Footnote ⁸⁵ Furthermore, there was increasingly concern that coal miners were suffering from respiratory disability that could not be traced to silica exposure.Footnote ⁸⁶ In 1936 the chief medical officer of the Silicosis Medical Board asserted that the claims for compensation made by coal miners in South Wales were rising. Refusal rates were also increasing, with up to 52 per cent of certificates refused in 1935.Footnote ⁸⁷

Normal breathing for miners

It was at this point in 1936 that the MRC was asked by the Home Office and the Mines Department to try and solve the problem of the disparity between visible tissue damage and subjective reports of illness. They were charged with investigating chronic pulmonary disease among coalminers, with a particular focus on the South Wales coalfields. The Medical Research Council had been funded by the government to instigate medical and biological research since 1911, and during the interwar years it was divided into numerous subsections which were endowed with significant freedom in their organization and research.Footnote ⁸⁸ The medical surveys undertaken from 1936 to 1942 were led by Dr Phillip D'Arcy Hart and Dr Edward Aslett, assisted by a large team of engineers, inspectors and pathologists.Footnote ⁸⁹ Retrospectively, D'Arcy Hart attributed the government intervention to the rise of compensation costs, concern for the health of the miners and the fact that ‘there was a war round the corner and they certainly did not want a dissatisfied coal-producing force’.Footnote ⁹⁰

The MRC selected an anthracite colliery for detailed investigation, and examined 560 of the men there, both radiologically and clinically.Footnote ⁹¹ The clinical tests involved included examination of the sputum, tuberculin tests and spirometric measurements of lung volume.Footnote ⁹² These lung volume determinations were supplemented by an exercise tolerance test, which categorized levels of ‘respiratory embarrassment’ into four possible subheadings.Footnote ⁹³ These groupings were then further categorized as either normal (class A) or abnormal (further divided by severity into class B or C).Footnote ⁹⁴ The degree of respiratory embarrassment was then measured against the medical history of the miner, which was provided by the mining inspector. The surveyors were satisfied that there was concordance between these two separately obtained measures of breathlessness.

The MRC created further standardized and standardizing measures in their classification of X-rays, dividing them into strictly defined categories: (a) normal, (b) reticulation, (c) nodulation, (d) coalescent nodulation, (e) massive shadows, (f) multiple fluffy shadows and (g–h) indefinite.Footnote ⁹⁵ The identification of the category of reticulation was particularly important because it identified the early stage of disease which resulted in disability in older miners.Footnote ⁹⁶ As Dr Gwent Jones (a GP working in Gower) explained in his 1943 report on silicosis, ‘Reticulation describes the X-Ray appearance of the fibrosis as it is first seen – it looks like the first snow on a window’.Footnote ⁹⁷ The MRC reports (published 1942–1945) were critical in that they proved that there was a link between length of exposure to coal dust and respiratory disability.Footnote ⁹⁸ This meant that there was now widespread medical acceptance of a disease due to coal dust that was entirely distinct from silicosis. Thus finally, in 1943, a disease due to coal dust was both legally recognized and duly compensated.Footnote ⁹⁹ The recognition of coalworkers’ pneumoconiosis resulted in an exponential rise in certifications under the Act, which overwhelmed the bodies responsible for their administration – the miners’ union and the Ministry of Fuel and Power.Footnote ¹⁰⁰

Calculations of partial disability levels were based primarily on assessing the functionality of the body in relation to continuing work: could the miner be disabled if he was still working? The Medical Research Council assessed the changes that X-ray investigation revealed in the miners’ bodies and concluded in its report that ‘the X-ray changes might be compatible at first with ability to work, but they were considered to represent a definite impairment of lung structure and to involve an increasing respiratory disability, manifested, for example, by shortness of breath’.Footnote ¹⁰¹ The MRC pondered the seriousness of this disability amongst the working population in its report and questioned whether hidden pulmonary abnormalities ‘among men still at work’ were of any consequence.Footnote ¹⁰² However, Dr Gwent Jones argued, ‘If the sufferer was only partially incapacitated and obtains a certificate for partial compensation, he is to the labour market only a part of a man, and being unskilled in any other trade he cannot compete with fit men in new occupations’.Footnote ¹⁰³

Such disputes regarding the potential for the disabled man to work permeated the Medical Research Council's investigations. As disability historians Turner and Blackie have recently explored, this kind of attitude reflected the reality for coal miners in the Victorian period, who would often continue to work while disabled.Footnote ¹⁰⁴ Jones's criticism of the compensation system highlighted that many men continued to work after certification, ‘whether he is a caretaker, or a part-time gardener, or just nothing, the “partial” is fortunate compared to the “full” who may be too short of breath to even lace his own boots’.Footnote ¹⁰⁵ Evaluating the relationship between work and disability was crucial to the new process of assessing disability and loss of function in the medico-legal field. Adjudicating disability was complex and involved new sets of standardized classifications for what changes constituted disability in relation to respiratory disease.Footnote ¹⁰⁶ Melling has confirmed that it was very difficult firmly to arrive at any kind of diagnosis using X-ray examination at this time: professional scepticism abounded, and techniques and interpretations were not standardized until nearer 1950.Footnote ¹⁰⁷ In this politically loaded context, in which new X-ray technology could not be fully trusted, the spirometer represented secure evidence of respiratory disease in numerical terms which could be utilized in the complex compensation network. As Braun has demonstrated, the spirometer offered ‘an objective marker of disability to industrial medicine’.Footnote ¹⁰⁸

However, using spirometry to diagnose pneumoconiosis necessitated a definition of normal with which to make the comparison. Gilson and Hugh-Jones explained in their MRC report of lung function in coalworkers’ pneumoconiosis, ‘The assessment of the effect of silicosis or pneumoconiosis on lung function implies a definition of normal with which to make the comparison. This is far more difficult than the scant reference [sic] in the literature would suggest.’Footnote ¹⁰⁹

The MRC's original clinical investigation used normal lung function values separately determined by Aslett, D'Arcy Hart and McMichael. However, the normal adult male subjects used as controls for these determinations were in fact taken from sixty-four members of ‘the normal members of the working population of an anthracite colliery in Carmarthenshire, the great majority being of Welsh parentage’.Footnote ¹¹⁰ The data sets used a normal standard set by apparently healthy miners rather than a non-mining control group. This would not have necessarily mattered if the investigation involved a longitudinal study – investigating the changing health of the same miners over a number of years. However, part of the point of this investigation was to work out if the environment was causing pulmonary disease and so used a cross-sectional method which compared the health of miners in different geographical areas (see Figure 1).

Figure 1.

Map of the South Wales coalfield marking the positions of the sixteen collieries of the inquiry. Medical Research Council, special report series no 243, Chronic Pulmonary Disease in South Wales Coalminers, London: His Majesty's Stationery Office, 1942, accessed at the National Archives, FD 41243, p. 11.

Only one mine was subjected to a full clinical investigation and the spirometry test here was clearly flawed, as it took its measure of normality from the very population in which abnormality was already apparent. This analysis is supported by Smith's study of ‘black lung’ in West Virginia, which has demonstrated that pathology in coal miners was considered normal for coal miners and that patient testimony as to their own condition was considered secondary to diagnosis. ‘What was “normal” for miners, including even a chronic respiratory condition, was by no means normal for the company doctor … to the extent that [if] their X-rays revealed the pathological changes now associated with coal workers’ pneumoconiosis, these too were considered normal – for coal miners’.Footnote ¹¹¹ Indeed, the reluctance to attribute diminished lung capacity to the effect of mining work was to continue. For example, in their 1955 report for the Medical Research Council, Gilson and Hugh-Jones compared D'Arcy Hart and Aslett's use of working miners as controls to a later (1950) study that used men who had never worked in dusty conditions as controls. The 1950 study ‘found a big difference in the maximum breathing capacity compared with men applying for compensation who had no evidence of silicosis on the radiography’.Footnote ¹¹² That is, men who had never worked in dusty conditions had greater lung capacity than those who had worked in dusty conditions, even though these men would not have been diagnosed with any respiratory disease. This difference was largely attributed to the constitutions of the men involved rather than their working conditions. Gilson and Hugh-Jones explained, ‘They concluded that the difference was psychogenic but it is possible that it was partly due to the effect of mining’.Footnote ¹¹³

Thus, if causation from dust or disease could not be established, then it followed that the problem must be related to the essential constitution of the miner. Similarly, attempts to clarify normal reference values were marked by attempts to explain variability in lung function through racial and ethnic difference.Footnote ¹¹⁴ The MRC's original investigation reported considerations of whether or not the Welsh were actually a separate racial group, and if so, whether that could account for their abnormalities in stature and high levels of lung disease, writing, ‘It is relevant here to mention the suggestion that the high incidence of pneumoconiosis in western Wales is associated in part with the racial composition of its inhabitants.’Footnote ¹¹⁵ This idea was rejected not because of environmental considerations but because a number of men at the colliery they examined had English parentage. Thus we see that innate biological causes and potential ethnic differences were sought in order to supersede social or environmental factors. Similarly, in the lung volume determinations compiled by Aslett, D’Arcy Hart and McMichael, there was consideration of the fact that the vital-capacity mean was lower in the normal subjects taken from the mines than it was in ‘previous series of normal males’ but that this difference was attributed to the smaller height and weight of the miners, ‘probably due to the Welsh racial characteristics’.Footnote ¹¹⁶

Attributing variability in lung function to racial difference was eventually enshrined in spirometric measurements by the MRC Pneumoconiosis Research Unit in South Wales – through the PRU's standards for ‘Average Normal Values for the Forced Expiratory Volume in White Caucasian Males’.Footnote ¹¹⁷ By 1974, the MRC had refined their measurements to allow them to ‘correct’ for racial difference using a scaling or correction factor of 13 per cent. This reinforced the idea that white lung function was normal lung function and, as Braun has established, this had far-reaching effects both in the compensation system and in the promotion of the thesis that inequality between the races was biological rather than environmental.Footnote ¹¹⁸