Notwithstanding several efforts, a satisfactory method of serological diagnosis of foot-and-mouth disease has not been arrived at. This uncertainty of serological methods delayed the discovery of the plurality of type of the virus, although the observations of epizootics and the irregular results obtained by active and passive immunisation suggested multiplicity of type. Stimulated by such observations, Vallée and Carré (1922) experimented with two viruses of foot-and-mouth disease, one of which was of German and the other of French origin. They were able to show by experimental infection, confirmed by subsequent testing for active immunity, that cases of foot-and-mouth disease with the same clinical course and symptoms could be caused by two distinct types of virus. These they called A (Allemand) and O (Oise). The only difference between these two types was their inability to produce reciprocal immunity. The existence of more than one type of virus has been confirmed in England by Stockman and Minett (1926), and by Bedson, Maitland and Burbury (1927); in Germany, by Waldmann and Trautwein (1926), and Trautwein (1927); in France, by Lebailly (1926), Olitsky (1927), and in Sweden, by Magnusson and Hermansson (1926).

A Microscopical study of the skins of mice painted with definite carcinogenic agents and with agents which appear to be incapable of exciting the production of tumours has, in the main, enabled us to confirm the observations of previous workers on the different histological changes which take place. A brief description of our findings will first be given.

Bacteriological diagnosis of the Enterica is only established with certainty on recovery of the infecting organism by recognised laboratory methods. In default, recourse must be made to a serological investigation into the agglutinating power of the patient's serum, when, theoretically, little difficulty ought to be experienced. In enterica suspects, unvaccinated or uninfluenced by previous enterica disease, demonstration of agglutinins reacting with the Bact. typhosum, paratyphosum A, B, or C in relatively high dilutions of their sera should be considered adequate evidence. In the vaccinated, elevation of agglutination titre—as determined by repeated examinations during the course of the disease—has been generally accepted as criterion for existence and type of infection. The principle of ascending dilutions, on which such “quantitative serum analysis” is based, is explained by the fact that in an infection with one organism a specific agglutinin is formed for that particular organism and group agglutinin is for other organisms closely related biologically; the specificity, therefore, of the agglutination reaction must be wholly dependent on the basis of dilution, the specific agglutinin being present in greatest quantity and operative in a range much exceeding that of the secondary group agglutinins. Reasonable as this view may seem in principle, it is far from easy of application in practice. Lack of accurate information as to the day of disease on which serum was taken, unreliable case histories in regard to vaccination or previous enterica infections, and inability of private practitioners to induce patients to submit to repeated blood collection constituted here primary difficulties.

The stability of the biological reagents used in routine immunological procedures is a matter of practical interest to the public health worker, and an attempt has been made in the following research to estimate the period during which the diluted toxin used in the Schick test for the estimation of susceptibility to diphtheria remains potent. In the early days of Schick testing, although Leete (1920) reported that a diluted toxin retained its potency for as long as 5 weeks, it has hitherto been considered inadvisable to use a toxin at a longer interval than 48 hours after it had been diluted to its proper strength. Glenny, Waddington and Pope (1928) and O'Brien, Okell and Parish (1928) have introduced a new diluent consisting of a solution of a combination of crystal borax 57, boric acid 84 and sodium chloride 99 parts. A 1·5 per cent, solution of this mixture is now used as a diluent and has the effect of sustaining the potency of the diluted toxin over a greater period of time. In our work over 400 persons have been tested with toxins made up according to this formula, a comparison being made in each individual between the reactions elicited by an aged toxin, stored for varying periods at room temperature or in the cold room, with those produced by a fresh toxin. Enough toxin was made up at the beginning of the experiment to last over a considerable period of time, samples being sent to us by post periodically together with batches of freshly diluted toxin. The testing of reagents was carried out immediately on receipt, the lower age groups being selected in any series of individuals as being likely to give the largest number of reactors. The actual testing was performed practically throughout by one of us (J. C. J. McEntee) so as to maintain uniformity of technique. Each pair of toxins was controlled by a single injection of inactivated toxin and the results were scrutinised at the 4th and 10th days, a record of the comparative intensities of the positives being made at the same time. The results are recorded in Table I.

During a recent investigation on the carrier problem as it occurs in diphtheria, which was carried out (under the auspices of the Scientific Advisory Committee of the Metropolitan Asylums Board) at the Northern Group Laboratory, North-Eastern Hospital, one of the first subjects considered was that of the bacterial flora of the carriers under examination, and of an adequate series of controls. It was suggested that possibly the flora of the carriers might differ (apart altogether from the presence of the Klebs-Loeffler bacillus) from that found in non-carrier persons of the same age. It was thought that some pathogenic organism might be found to be constantly present in the nose or throat flora of carriers and not in controls, and that this might be exerting an influence on the Klebs-Loeffler bacillus by allowing it to survive in the infected region for prolonged periods. If such were the case it was hoped that an elimination of the organism or organisms concerned would go a long way towards clearing up the carrier condition.

This investigation of the incidence of tumours of the respiratory tract in Leeds was prompted by a paper read by Duguid before the Pathological Society of Great Britain and Ireland in January 1927, and published in the Lancet later in the same year. He analysed all the available post mortem records of the Manchester Royal Infirmary and showed that the incidence of intrathoracic cancer at autopsy in Manchester has steadily increased during the period of years 1886–1926 from 1·58 per cent, to 2·57 per cent.

B. dysenteriae (Sonne Type III) may be separated from the dispar group by the fact that it is indol negative and zylose negative. It is usually inagglutinable when freshly isolated but will remove all agglutinins from a Sonne serum. B. dysenteriae (Sonne Type III) is a serological entity and can readily be distinguished from B. dysenteriae Flexner and from the dispar group. Eleven strains of B. dysenteriae (Sonne Type III) have been isolated and examined, along with standard cultures of this group of organisms.

In the course of a paper by the present writers (this Journal, xxv, 336–53) an attempt was made to assess the relative importance of selective mortality on the one hand and sub-lethal infection on the other in increasing herd resistance to subsequent exposure to infection. The subject was further considered by one of us (E.M.N.) in a later report (this Journal, xxvi, 19–27).

1. Bacteriological examination from the tonsils and post-nasal space in forty-six cases of acute and sub-acute rheumatism resulted in streptococci alone being isolated.

2. The streptococci isolated fell into three groups, S. mitis, S. salivarius, and eleven strains of S. cardioarthritidis.

3. Comparison of the strains of S. cardioarthritidis with strains isolated in America show them to be closely related.

4. No evidence was found of an exotoxin.

5. Evidence was found of the presence of an endotoxin or lysate which produces an antitoxin.

6. Intravenous inoculation of the lysate into rabbits appears definitely to affect the heart muscle and lungs, and to some extent the liver and kidneys.

Organisms which appear to be morphologically, culturally, and serologically identical have been recovered in four separate outbreaks of illness suggestive of dysentery.

They have been readily isolated in considerable numbers from all cases examined in the early phase of the attack.

When 1 per cent, peptone water is used as a basis for carbohydrates these organisms usually leave lactose, mannite, dulcite, and saccharose unaffected but ferment glucose and maltose with the production of acid. Barely, a minute amount of gas is also produced from glucose and occasionally slight acid and gas from dulcite. On the other hand, when Lemco broth (Dudgeon and Pulvertaft, 1927) is used as a basis, glucose, dulcite, and maltose are consistently fermented with the production of acid and gas.

Agglutination tests against normal sera and against anti-sera prepared from the dysentery and paradysentery bacilli and from B. paratyphosus A are uniformly negative but strains of the organism derived from all four sources are agglutinated to approximately the same titre by an anti-serum prepared from one of them although this anti-serum has no effect on three organisms whose reactions present some degree of similarity.

The organisms do not appear to be toxic for rabbits.

With all patients affected in these outbreaks, whose blood was available for examination, the serum has shown the presence of specific agglutinins which could not be demonstrated in normal serum.

On the whole, therefore, the evidence suggests that these organisms may be responsible for the diseased condition.

Invisible infective agents may be divided into: (1) true, ultramicroscopic, living viruses, which do not arise de novo and, so far as is known, are not ubiquitous; (2) transmissible infective agents which arise de novo and are propagated through living cells, but are not themselves living organisms; (3) stimulants to variation which arise de novo, are not transmissible, and are not living organisms.

Class (1) is not represented in malignant disease. “Bacteriophage” is a representative of class (2); very probably the infective agent of fowl sarcoma comes under the same category, and possibly some important human diseases of doubtful aetiology. There is no satisfactory evidence that mammalian malignant disease is related to class (2); its causation, according to the “chronic irritation” theory, must be attributed to influences comprised within class (3).

The stimulants to variation in class (3) depend for their effectiveness upon the unstable energy of living matter. The changes which they produce are “biological” in the sense that they are changes of chemical constitution which could not be obtained without the aid of vital processes.

Regulation of normal growth in the animal body means regulation of the cell's facilities for obtaining energy. I think it is misleading to regard it as a forceful restraint (or stimulus) upon the cell's inherent capacity for unlimited growth.

The assumption, borrowed from “natural immunity” towards bacteria, that there is in the animal body a natural principle which destroys frequently occurring foci of incipient malignancy is also unsubstantiated and misleading.

During the latent period, certain cells, which subsequently grow into a neoplasm, lose their capacity to respond to inhibitory systemic influences. This change is brought about by local and not by systemic causes.

As regards the special class of tumour derived from cells which have been displaced in foetal life, long residence in an abnormal situation does not appear to be equivalent to the ordinary latent period; but it may have had the effect of increasing their susceptibility, so that, if exposed to chronic irritation, the cells would more readily lapse into the latent period predisposing to malignancy.

It is known that the various tissues of the animal body differ in their degree of susceptibility to the precancerous change. This is a cellular characteristic; so also is the difference in the susceptibility of one animal as compared with another. It is not a question of difference in a hypothetical humoral property of “systemic resistance.”

On the termination of the latent period by a fresh stimulus to proliferation, certain cells commence active growth and are incapable of responding to systemic inhibitory influences. These conditions seem sufficient for the origin of an innocent neoplasm. But something more is required to explain malignancy, because the malignant cell is essentially different from the cells in a benign tumour.

About the actual cause of the change to malignancy one can only offer conjectures. I have suggested a way in which the change may possibly be produced through the agency of the local endothelium and the autogenous formation of antibodies.

On taking a broad view, the change into the malignant variant is not something unique; equally remarkable changes are to be found in the properties of bacteria. In both cases the facts have to be accepted, at present, without satisfactory explanation of the conditions which gave rise to them. One finds with bacteria that degradation or “roughness” may be a phase preparatory to the acquirement of new properties, just as the degradation of cells in the latent period seems to be a requisite preparation for acquiring the new property of malignancy. But the actual steps involved in the change from a bacterial saprophyte to an invasive parasite are as difficult to understand as are the processes involved in the conversion of a normal animal cell into its malignant variant.

Throughout the study of cancer it is very desirable to maintain a clear distinction between cause and effect. For example, the enzymes peculiar to cancer are not the cause of cancer but the effect of the biological change which produced the cancerous cell.

Dans trois courtes notes, j'ai décrit précédemment des variations très particulières que présentent certaines souches de bacilles fluorescents, et j'ai montré comment on peut arriver à les reproduire in vitro dans des conditions déterminées. Je compte reprendre ici cet exposé des faits et des considérations théoriques qui en découlent.

1. The bacteriological examination of the throat or nose in 100 cases of scarlet fever on admission to hospital showed the following incidence of the different serological types of streptococci. Of 91 cases yielding positive results on the first examination, haemolytic streptococci of Type 1 were found in 8, Type 2 in 14, Type 3 in 26 and Type 4 in 12; the remaining 31 fell into the heterogeneous group. In the 9 patients who gave a negative swab on admission a later test showed Type 1 in 2 cases, Type 2 in 4 cases, Type 3 in 1 case and heterogeneous strains in 2 cases.

2. The heterogeneous group comprised individualistic strains, none of which occurred with sufficient frequency to form a fifth type.

3. In 50 out of the 100 cases examined at weekly intervals the type of streptococcus remained the same throughout the attack.

4. In 50 cases there was a change of type during the course of the disease; a second type appeared in 38, a third in 10 and a fourth in 2.

5. The change of type was considered to be a reinfection since it appeared most often in the youngest children and after the 3rd week of treatment; the source of reinfection was traced in two instances.

6. In 3 patients, in whom the Dick reaction remained positive, the appearance of the new type coincided with a second attack of clinical scarlatina.

7. Of the 50 patients in whom no change of type was demonstrated 20 still carried the haemolytic streptococci on discharge after periods in hospital ranging from 4 to 8 weeks.

8. Of the total 100 cases there were on discharge 49 throat carriers of haemolytic streptococci and 6 nose carriers. None of the 55, so far as was ascertained, gave rise to “return cases” of scarlet fever.

9. There was evidence of correlation between serological type of streptococcus on the one hand and severity of scarlatinal attack and occurrence of complications on the other. The importance of this in hospital practice is emphasised.

10. The Dick test and Schultz-Charlton reaction were carried out on all cases in the series; the results indicated that the four serological types have different immunological values.

11. The evidence in favour of qualitative as opposed to quantitative differences in toxin production by the different types is discussed.

If a medium containing either 1 per cent. ammonium succinate or 1 per cent. ammonium fumarate together with certain inorganic salts be inoculated with B. pyocyaneus and incubated aerobically at 37° C. a vigorous growth of the organism will ensue, the rates of growth in both cases not being markedly different from each other. If the growth be allowed to proceed for a fortnight, analysis of the media shows that essentially similar products (mixtures of the lower fatty acids) have been produced in both cases. If the growth be allowed to proceed for not longer than three days, analysis shows that in the succinate medium over 80 per cent. of the succinic acid has not been utilised, whilst in the other medium the entire fumaric acid has disappeared, giving rise in its stead to pyruvic acid which is further utilised as growth proceeds(1). Quantitative data support the view that the breakdown of succinic acid occurs through the intermediate production of fumaric acid, the rate of fermentation of fumaric acid being greater than that of succinic acid, so that fumaric acid is not detected among the products of fermentation of succinic acid. If this view is true, it should be possible to show that B. pyocyaneus has the power of oxidising succinic acid to fumaric acid. It is clear that the proliferating organism cannot be used to demonstrate this experimentally, for the fumaric acid is utilised as quickly as it is formed. Hence it is necessary to use the organism in such a condition that proliferation is completely (or almost completely) eliminated. Under such circumstances the fumaric acid will accumulate and its detection will be made possible.

In 1917 and 1918 Tunnicliff announced that she was able to obtain cocci from the blood of cases of measles in the pre-eruptive and eruptive stages of the disease. It was claimed that anaerobic methods were necessary for their isolation, but after the initial growth appeared these organisms could be sub-cultured aerobically. Later, this worker (Tunnicliff, 1919) found a similar organism to be the predominating species in cultures obtained from the sputum of acutely ill cases. Caronia (1923) reported that he was able to isolate with great regularity a small diplococcus from the blood of measles cases by using the Tarozzi-Noguchi medium.

The results of an inquiry into colds and slight influenza—held by me with the obliging collaboration of 7000 informants in the Netherlands from September 1925 till June 1926—do not contradict the hypothesis propounded in the introduction, that various respiratory diseases depend upon a disturbance in the thermo-regulation, in consequence of which the body becomes receptive to commensal infection.

In the first place a proportionally equal number of colds was reported at the same time from the various parts of the country during the period of observation, while the increase and the decrease of these colds ran parallel to the falling and rising of the temperature of the air. Further, when calculating the figures from large and from small families, it was proved that the members of small families have no lesser chance of infection than the members of large families.

This joint result tells against the contagiousness of colds in the period of observation.

The outbreak in September stood alone; the preceding period had not been marked by a low average temperature but by a series of cold nights. During the following month the occurrence of colds was accompanied by the mortality from old age and by the joint mortality from bronchitis and pneumonia.

An increased mortality from pneumonia in March–April, linked up with a moderate lowering of the temperature of the air, was not accompanied by “old-age mortality” and only moderately by “colds” it went together however with an increased mortality from influenza. The influenza cases of the inquiry too had increased by that period of time. So the influenza showed itself as a parasitic infection, which takes its own epidemic course. Still the possibility remains of the virus, at times of reigning influenza, having also widely spread among the healthy. At any rate the idea that catching cold reduces resistance to influenza or pneumonia is supported by the data.

The opinion obtained from the results of the inquiry, that most colds and pneumonia, as well as many cases in which old age has been given as the cause of death, are founded on a disturbance of the thermo-regulation, has drawn attention to physiological oscillations of the temperature of the body in relation to that of the temperature of the air. As the thermo-regulating system is not able to fix the temperature of the body completely, even under normal conditions, but allows a certain poikilothermia, it is clear that by a considerable drop in the temperature of the air these oscillations of the temperature of the body become so large that they may cause a disturbance.

The prophylaxis of the diseases from catching cold will have to be directed towards the application of “passive” prophylactics (for preserving and supplying heat by imminent cooling), as well as of “active” prophylactics (raising the production of heat by the body).

For some years one of my principal interests has been to study, in collaboration with my colleagues, E. M. Newbold, W. W. C. Topley and J. Wilson, the epidemiological phenomena observable in communities of mice exposed to risk of infection. In this work we have often found it convenient to summarise part of our results under the form of what we call a Life Table. We treat the entrants to our communities as live-births and determine the rate of mortality prevalent in the community over a certain epoch for each day of life, in the familiar life-table form. The result has a formal resemblance to a life table, but, from the nature of the case, it can have little or no bearing upon the course of events in a normal community. Naturally, however, one desired to set up some normal standard of mortality for the animal species used and, having obtained some scanty data, one was led to speculate further upon the biology of the so-called “laws” which have been from time to time proposed to describe the course of mortality in man. In this paper, I have brought together the imperfect results of such study as I have been able to make. Their practical value, from the point of view of the description of human mortality, is, it need hardly be said, negligible, while as a contribution to the history of “laws” of mortality what is omitted is perhaps as important as what is discussed. I have, however, felt justified in printing this essay in the hope that it might be accepted as a tribute in piam memoriam of my friend and colleague John Brownlee. The title of one of Brownlee's papers—“The Biology of a Life Table”—was the inspiration of much of his life-work. He approached the problem with an erudition, both biological and mathematical, to which I have no pretensions and, had his power of exposition been equal to his natural sagacity and learning, there would have been small need of any other writer.

(1) The concentration of small-clumping (O) typhoid agglutinin in the serums of a group of recently inoculated persons was found to be, on an average, distinctly higher than that of a group of uninoculated persons.

Additional proof that this is the result of the inoculation is given by tracing the curve of production of “O” agglutinin in a healthy adult immediately after inoculation.

(2) The serums of healthy persons show a moderate but extremely variable power of clumping typhoid “O” suspensions. Expressed as a titre, the normal limit varies between 1 in 50 and 1 in 200, according to the sensitiveness of the suspension used. Expressed in standard units of “O” agglutinating power the normal limit is 10 standard “O” units.

(3) Methods of preparation of permanent suspensions for the estimation of “O” agglutinin are discussed and Felix's recommendation of the alcohol method is confirmed. The agglutinability standardisation of suspensions of this kind is described.

(4) Broth suspensions treated with 0·1 per cent, formalin, such as are used for the ordinary Widal reaction, are shown to be capable of detecting “O” agglutinin, but to be less suitable for its estimation than alcohol suspensions.

(5) The place of small-clumping “O” agglutination in the diagnosis of typhoid fever is discussed, and a method of performing the combined “H” and “O” test in inoculated persons is suggested, wherein a compromise is effected between the customary quantitative measurement and Felix's qualitative “one-dilution” method.

1. In B. typhosus, B. paratyphosus A and B, and B. enteritidis Gärtner, low concentrations of phenol and formaldehyde produce a definite inhibition of the 0 agglutination, while the H agglutination is unaltered—a fact already established many years ago in the case of B. proteus X 19.

2. Alcohol, even in high concentrations, has no such inhibitory effect.

3. Therefore, suspensions preserved in the usual way with phenol or formalin are not adequate reagents for the qualitative serum analysis in enteric fevers or for the usual diagnosis test in typhus fever.

4. Phenol and formalin suspensions are responsible for negative results of the Widal test in cases of enteric fevers which show only the 0 immune body in the serum; such cases form a considerable percentage of the total especially in typhoid fever.

5. As a routine measure in the diagnosis of enteric fevers, it is suggested that two preserved suspensions of each organism be used:

(1) an alcoholic suspension (like that of Bien and Sonntag in typhus fever) as a reagent for the 0 agglutinin, and

(2) the usual phenol or formalin suspension as a reagent for the H agglutinin.

6. The nature of the described phenomenon of inhibition is not, as yet, entirely clear.

In the early records of mortality there was much confusion between scarlet fever and diphtheria. According to Hirsch, after scarlet fever had been clearly differentiated from measles about the middle of the eighteenth century a new error was introduced into the doctrine of scarlet fever. Emphasis was placed on the inflammatory process in the throat which frequently occurs in scarlet fever, and this led to its being confused with diphtheria.