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344 EDITORIAL ARTICLE.
such growths. They also show that without any treatment whatever such papillomata may disappear by a process of gradual shrinking and absorption, and they suggest the thought that the credit claimed for some methods of treatment may be undeserved.
Lastly, the experiments indicate, though, owing to their small number, they cannot be said to prove, that after disappearance of a first crop of papillomata the animal is left in a measure protected against a second infection of the same kind.
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THE RELATIONSHIP BETWEEN HUMAN AND BOVINE TUBERCULOSIS.
SINCE the identity of human and bovine tuberculosis was first demonstrated very diverse opinions have been expressed by medical authorities as to the frequency with which the disease is communicated from the one species to the other. For a number of years after Koch's discovery of the tubercle bacillus the view that" human phthisis frequently comes from the butcher's stall" was rather widely adopted, and this opinion was in very large measure responsible for the crusade originated against tuberculosis of cattle. Within the last few years, however, the view which has been steadily gaining ground among authorities on questions of human sanitation is, that the immense majority of cases of human tuberculosis originate in human sources of infection, and that if any great reduction in the present prevalence of the disease is to be brought about prophylactic measures must be directed against the spread of the infection from man to man. An important contribution to this question has recently been made by Sir Rirchard Thorne in his Harben Lectures on the Administrative Control of Tuberculosis, and it is of interest to note the estimate which he has formed of the dangers incurred by the public from the consumption of tuberculous meat and milk.
At the outset Sir Richard Thorne reviewed the measures which had been adopted during the last forty-five years in the control and prevention of the different forms of tuberculosis, and the results achieved as shown by certain vital statistics prepared for the Royal Commission on Tuberculosis by Dr Tatham. From these statistics it appears that during the last forty years there has been a very notable decline in the death-rate from tuberculosis among human beings in this country. This decline has been constant, and it applies to all forms of tuberculosis collectively, but it has been most
EDITORIAL ARTICLE. 34-5
marked in the case of phthisis, which at certain periods of life has experienced a reduction of 60 per cent.
These highly satisfactory results were mainly ascribed by the lecturer to administrative measures which had secured increased movement of air and greater access of light around and within human habitations, and which had led to a lowering of the level of subsoil water in our towns and in the neighbourhood of villages and dwellings. Sir Richard Thorne points out that all this had been effected before the discovery of the tubercle bacillus had led to any special action based on bacteriological knowledge, and he anticipates that if as much can be effected during the next half century death from pulmonary tuberculosis at many age periods will have been entirely abolished in this country.
It would be of immense interest to know how cattle have fared with respect to the same disease during the half century which has brought such a remarkable decline in the death-rate from human consumption. Unfortunately, there are absolutely no reliable data on which to found a comparison. At the present time many people have adopted the opinion that bovine tuberculosis is vastly more prevalent than it was half a century ago, but there does not appear to be sufficient evidence to warrant any opinion on the subject. In this matter it is very easy to drop into error (I ) by forgetting that we are only now heginning to acquire an accurate notion of the number of cattle affected with tuberculosis, and (2) by overlooking the fact that death-rate and prevalence are not the same thing.
The use of tuberculin on live cattle, and rigid post-mortem inspection of apparently healthy cattle, appear to justify a \"ery high estimate of the present prevalence of tuberculosis among adult bovine animals in this country-probably not less than 30 per cent., but there is no reliable information as to the number of cattle that die annually from the disease. A comparison between human and bovine tuberculosis in this respect, even if we had reliable figures, would be vitiated by the fact that tuberculosis in cattle is seldom allowed to run a natural course when it threatens to end in death. But even if we reckon with the fatal cases those in which the animal is slaughtered because of tuberculous symptoms, the death-rate from tuberculosis among cattle over the whole country is not very great.
\Ve have said that there is no reliable information upon which one may base a comparison between the present and the past with regard to the prevalence of tuberculosis in cattle. but in a recent article on the subject 1 M. Leclainche attempts to show that the disease has spread in an alarming manner even within the last ten years. In support of this view statistics from various slaughter-houses are cited, showing, in the case of Leipzig, for example, a rise from 11'1 per cent. in 1888 to 33'02 in 1895. These figures we believe to be entirely
1 "Revue ,Ie la tuberculose," ]898, p. 307.
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fallacious as an index to the prevalence of the disease, since it is almost certain that during the period referred to the search for tuberculous lesions in public slaughter-houses has become much more severe. M. Leclainche cites this country in evidence of the spread of the disease, and says: "Great Britain has seen its finest breeds successively decimated and threatened with complete destruction." This is a very exaggerated estimate of the state of affairs; at least, if it is not, the owners of tuberculous herds in this country have been remarkably successful in concealing their losses. No doubt many of our finest herds contain a large proportion of tuberculous animals, but the fact has been discovered by the tuberculin test, and not by the death of any considerable number of the animals. In fact, in this matter we are probably no worse off than France itself. Only a few years ago, in a Bill for dealing with tuberculosis laid before the French legislature, the proportion of Frcnch cattle affected with the disease was officially estimated at I per cent.; but M. Lcclainche now admits that the tuberculin test has revealed from 50 to 80 per cent. of affected animals in herds previously thought to be free from the disease, and he places the number of animals attacked in the whole of France at somewhere between 10 and 20 per cent.
It thus appears that we have statistics indicating the death-rate from human tuberculosis, but not the proportion of human beings attacked; while, on the other hand, we have some fairly reliable indications of the number of cattle affected with tuberculosis, but none as to the number of deaths caused by the disease. May one assume that the very gratifying reduction of the death-rate from tuberculosis among human beings has been accompanied by a corresponding decline in the number of persons attacked? It may at first appear that this question must have an affirmative answer, but further reflection makes the question more doubtful. It certainly appears to be possible that the decline in the death-rate from human phthisis may be in part, perhaps even mainly, due to a more rational and successful treatment of the clinically tu berculous. Let us suppose for a moment that this explanation of the figures is rejected, and that it is maintained that the decline in the number of persons attacked has been eq ual to the decline in the death-rate since 1851. vVe have said that statistics regarding the present prevalence of the disease are lacking, but an estimate of the number of persons attacked may be based on the number of cases in which tuberculous lesions are detected in the bodies of persons submitted to post-JIlortem examination in hospitals. A pathologist of large experience estimates that at the present time such lesions are present in about 30 per cent. of the bodies examined -a proportion which may at first sight appear incredible, but which is no more surprising than to find a like proportion of animals reacting to tuberculin in an apparently healthy herd. Hence, it would appear that, if the decline in the prevalence of the disease has kept
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pace with the diminution in the death-rate, about 50 per cent. of the inhabitants of England and Wales must have been tuberculous half a century ago.
The connection between damp soil and phthisis was first put forward by the late Sir George Buchanan, Sir Richard Thorne's predecessor at the Local Government Board. Buchanan went so far as to say that" wetness of soil is a cause of phthi .. is to the population living upon it." This was before the discovery of the tubercle bacillus, and before it had been recognised that tuberculosis is a purely contagious disease. If it were an established fact that draining of the soil, without any other change in the circumstances affecting the spread of phthisis, is always followed by a decline in the death-rate from that disease, we should have to recognise a relationship of cause and effect between dampness of soil and phthisis, even although we could not understand the exact way in which the dampness of soil induced the disease in persons living on it. But at the present day it cannot be admitted that the quality of the subsoil has the importance which Buchanan ascribed to it as a factor in the etiology of phthisis. A wet subsoil cannot cause phthisis without the tubercle bacillus, and when the conditions and habits of life of the population are favourable to infection the disease will spread 011 the dryest of subsoils. These statements are incontrovertibly true for tuberculosis of animals, and they probably hold good for human phthisis also.
Sir Richard Thorne called attention to the fact that while during the last half century there has been a remarkable decline in the deathrate from phthisis, there has not been a corresponding diminution in the number of deaths returned under the head of tabes mesenterica. At most ages the decline under that head has been quite trivial during the last half century, and there has been an actual increase in the rate of death from this form of the disease in children under one year of age. The lecturer boldly asserted that the explanation of this remarkable fact is to be found in the circumstance that phthisis is mainly due to aerial infection, and is therefore influenced by improvements in the direction of ventilation, lighting, etc., while tabes mesenterica is caused by alimentary infection through the
'medium of meat and milk, and is therefore unaffected by such sanitary measures. Tuberculous meat he believes to be only in a minor degree responsible for cases of tabes mesenterica in the human subject, but he considers the loss of child life from the consumption of tuberculous cow's milk to be appalling. This is a very grave indictment of the milch cow as an agent in the dissemination of tuberculosis among human beings, and if it were proved it would justify the introduction of the most energetic measures against bovine tu berculosis.
Apparently Sir Richard Thorne's charge against tuberculous
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milk might be formulated somewhat as follows. During the last fifty years there has been a marked decline in the death-rate from tuberculosis due to aerial infection (phthisis). During the same period there has been only a slight decline in the death-rate at all ages from that form of tuberculosis which is ascribable to alimentary infection (tabes mesenterica), and among children under one year of age there has been a notable increase in the mortality from that form of the disease. This increase in the proportion of deaths in young children returned under the head of tabes mesenterica has been coincident with a large increase in the consumption of cow's milk as an article of human food. The use of tuberculous milk is therefore the main cause of tabes mesenterica in children.
There are several obviously weak points in this indictment. The first of these touches the application of the term tabes mesenterica by medical men in certifying the cause of death. Dr Tatham, who presented the statistics on which the charge against milk is framed, says 1: "Tabes mesenterica is an indefinite but time-honoured term, under which are probably included, in addition to tubercular affection of the mesenteric glands, peritoneum, and intestines, a considerable but unknown number of ill-defined ailments in which wasting and diarrhc:ea are prominent symptoms. This disease in its fatal form affects young children almost exclusively."
Now, when it is remembered that all except an inconsiderable fraction of cases of so-called tabes mesenterica are certified without a post-mortem examination, it becomes impossible to repose great faith in the Registrar General's returns so far as they pretend to be a record of the deaths from alimentary tuberculosis. It cannot even be said to be improbable that the majority of the cases returned under this head have nothing whatever to do with tuberculosis. And when one examines with a little more detail the figures given in Dr Tatham's tables one finds certain variations in the incidence of the mortality from the different forms of tuberculosis that are wholly inexplicable on the view that the terms have been consistently employed throughout, have embraced all the deaths from that form of the disease, and have not included many deaths from other diseases. For example, in the decennium 1851-60 the deaths returned under the head of phthisis in children under one year of age numbered 2032 per million births, and in the period 1861-70 they had fallen to 1370 per million births, but during precisely the same period there was scarcely any decrease in the death-rate from phthisis at thirty-five to forty-five years of age (4091 per million living ill 185 I -60 and 4026 in 1861 -70). It is very difficult to understand what were the conditions that effected such a great reduction in the mortality from phthisis among infants between 1860 and 1870,
1 Report of the Royal Commission on Tuberculosis, p. 357.
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and yet were without any sensibly ameliorating influence 011 the mortality from phthisis at middle life.
The statistics relating to tabes mesenterica are no less puzzling. Take for example the followi'ng:-
Table showing JI
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fit in with the view that tabes mesenterica comes mainly from the milking pail, we would have to assume that there has been a great falling off in the consumption of cow's milk in Glasgow during the last twelve years, or a great decline in the number of tuberculous cows contributing to the milk supply of that city. We believe there is no evidence to lead one to suppose that either of these things has happened.
The conclusion at which we arrive is that the Registrar-General's returns under the head of tabes mesenterica cannot with confidence be accepted as an index to the proportion of human tuberculosis contracted through drinking the milk of tuberculous cows. It is almost certain that the term covers such a large number of deaths from other causes as to entirely vitiate the statistics. Strong evidence in support of this view is furnished by a chart which Dr Tatham submitted to the Royal Commission on Tuberculosis to show the annual fluctuations in the death-rate from tabes mesenterica and diarrhcea during the last twenty years. The parallelism between the two lines is very striking, and almost compels one to believe that while some practitioners return cases of death following diarrhcea and wasting under the head of diarrhcea, others return them as tabes mesenterica.
But even if one could accept all the cases returned under the head of tabes mesenterica as undoubted instances of tuberculosis affecting the abdominal organs, it would not be justifiable to maintain that all such cases had their origin in tuberculous milk. In the households of the very poor the circumstances which contribute to aerial infection with tuberculosis must also carry with them some risk of food contamination, and consequently of alimentary infection; and some customs, such as kissing, tend specially to the infection of human beings by way of the alimentary canal. Taking all these facts into consideration, we should prefer to frame the indictment against milk, not on anything disclosed by the Registrar-General's statistics, but on the ground that tuberculosis of the cow's udder is not a rare disease; that the milk of a tuberculous udder when tested by experiment on animals is invariably infective; that at the present time there is hardly any legal obstacle to the sale of such milk; and that such milk is beyond doubt being sold every day in many parts of this country. We may not be in a position to say precisely what proportion of cases of the human disease are caused by milk, but it is impossible to doubt that some cases originate in that way, and the public have surely a right to demand that if there are any reasonable measures by which this danger can be averted or minimised, they Qught to be put into force without further delay.
