Since the early work of Nuttall (1888), Buchner (1889), and others first disclosed the bactericidal property of normal serum, a considerable amount of attention has been devoted to this important biological phenomenon. The literature (which has been reviewed recently by Knorr, 1929) lacks, however, a comprehensive and co-ordinated study of the subject, and in fact presents a good many confusing data in regard to the nature of the active principles concerned and their immunological significance.

1. In a group of boys, revaccinated 12 years after primary vaccination in infancy, 37 per cent, gave “immune” reactions to vaccine virus.

2. Immune reactions were more than twice as common in those boys with two or more old vaccination scars than those with one.

3. When the number of scars was held constant there was no tendency for groups with large scars to be more immune than those with small scars.

4. The average area of a single old scar was smaller in the “immunes” than in the rest of the group.

5. The substitution of a vaccination technique consisting of one insertion of lymph with a minimum of trauma, for two or three insertions by “crosshatched” scarifications was followed by nearly a threefold fall in the recorded vaccinia morbidity, and a halving of the number of days' sickness attributed to vaccinia.

The occasional occurrence of ”paralytic accidents” during the course of antirabic inoculation is well recognised as an unfortunate complication of that therapeutic measure. The cases have to be distinguished from the rare instances of paralytic rabies in which, usually after extensive bites from rabid wolves, the disease assumes an unusual form and in which the virus can be recovered from the central nervous system. The paralytic accidents on the other hand are in no way related to the date or severity of the original injury—on occasion the suspected animal has later been proved healthy—but are definitely associated in time with the commencement of the treatment; almost all occur within 7–23 days of the first inoculation, and fatal cases show no rabic virus in the nervous structures.

1. Altogether 117 strains of Brucella, belonging to different types and isolated from different parts of the world, have been examined by the thermoagglutination, salt agglutination, acid agglutination, and specific serum agglutination tests.

2. The results obtained by the thermo-agglutination and the serum agglutination tests are in close agreement; there is a fairly high degree of correlation between these tests and the acid agglutination test, and a rather lower correlation with the salt agglutination test.

3. Generally speaking, a strain which is highly thermo-agglutinable is frequently agglutinated by salt, is usually agglutinated strongly by acid, and reacts to a paramelitensis, but not to an abortus serum.

4. A strain which is moderately thermo-agglutinable is seldom agglutinated by salt, is frequently agglutinated by acid, and reacts either with an abortus or a paramelitensis serum, or with both sera.

5. A strain which is not thermo-agglutinable is not agglutinated by salt, seldom reacts markedly to acid agglutination, and is generally agglutinated by an abortus, but not by a paramelitensis serum.

6. There remain, however, a certain number of strains, particularly of the porcine and bovine abortus types which, though non-thermo-agglutinable, inagglutinable by salt, and reacting only with an abortus serum, yet show some degree of acid agglutination.

7. Of the twelve porcine strains examined only one strain was strongly thermo-agglutinable; of the forty-seven bovine strains only two were strongly thermo-agglutinable, a further two showing a milder degree of thermoagglutinability; of the forty-seven melitensis strains eight were strongly, and thirteen were moderately thermo-agglutinable; while of the eleven paramelitensis strains ten were strongly thermo-agglutinable.

8. These results are taken to indicate, in accordance with the suggestion made by certain previous workers, that those strains which are non-thermoagglutinable, are not agglutinated by salt, and are agglutinated by an abortus but not by a paramelitensis serum, represent the smooth form, while those strains which are strongly thermo-agglutinable, are frequently agglutinated by salt, and are agglutinated by a paramelitensis but not by an abortus serum, represent the rough form.

9. If this interpretation is correct it will be noticed that the great majority of the porcine and bovine strains examined were of the smooth type, that nearly half the melitensis strains were partially or completely rough, while all but one of the paramelitensis strains were rough.

10. Whether melitensis strains have a greater tendency than abortus strains to undergo the smooth to rough transformation it is difficult to say with certainty, but the reports in the literature and the observations in the present paper render this probable.

11. By serial passage through broth at 5-day intervals, it is possible to transform smooth strains of all three types into the rough form. This transformation appears to occur more readily and to proceed further in a given time with melitensis than with abortus strains; but since only three strains of each type were examined, the results may have been determined as much by chance selection of strains as by any greater inherent tendency of the strains of the melitensis type to undergo variation.

12. It is clear that none of the tests employed suffices to differentiate individual strains of abortus and melitensis. The thermo-agglutination test and the agglutination test with specific smooth and rough sera do, however, enable a differentiation to be made between smooth and rough strains of all types.

13. In the present paper no attempt has been made to distinguish abortus and melitensis strains by specific agglutination and absorption tests. The general failure of workers hitherto to obtain any clear-cut serological distinction between these types may possibly be due to the fact that many of the strains with which they worked were either partially or completely rough. Since the rough antigen seems to be more or less alike in strains of all types, it is clear that its presence would tend to obscure any difference that might exist between the smooth antigens of the different types. If such a difference does exist it is probable that it will be elicited only by a comparison of absolutely smooth strains.

Experiments were carried out on rabbits, guinea-pigs and monkeys to test the immunity produced by vaccinia virus killed with heat, phenol or formalin. Before use, the vaccines were rigorously tested for their inactivity by a method of inoculation and triple passage in series. The test of immunity was quantitative.

The rabbit experiments gave equivocal results but indicated that a slight immunity was produced in some cases. In guinea-pigs more success was obtained: they could be protected against one to ten minimal infecting doses and showed a partial immunity to stronger tests. Monkeys were only tried in one experiment in which a weak vaccine was used. This did not protect them.

The superiority of guinea-pigs for this kind of work is discussed as also the bearing of the results obtained with them on the nature of immunity to vaccinia virus.

In the annual report of the Chief Medical Officer of the Ministry of Health for 1925 (p. 22) the incidence rates of notifications of pneumonia in four-weekly periods are compared for large geographical groups in England and Wales. These rates show the divergence between the north and north-west and the remainder of the country, and also the fact that the north-west (Lancashire and Cheshire) usually compares badly with the north. During 1923 “in none of the thirteen periods was the rate for the north-west less than 15 per cent, in excess of the all-England rate and in ten it was equal to or greater than the rate for the north.” That these remarks still apply may be seen from the figures for 1930 (Table I). If one compares some of the large Lancashire towns with London the contrast is even greater (Table II). The towns giving the largest number of notifications of pneumonia are Liverpool and Manchester. These towns alone contributed 48 per cent, of the total number of notified cases of pneumonia in Lancashire during 1930. Their combined population forms about 30 per cent, of the total. Great caution is, however, required in drawing deductions from rates of notification of pneumonia, as considerable differences exist between one place and another in the extent to which the obligation to notify is complied with. Mortality rates provide a sounder basis of comparison.

The object of a paper by Fry (1930, p. 313)1 was “to ascertain…the relation of syphilis to malignant disease as determined by the Wassermann reaction.” The conclusion reached (p. 322) was: “In general, from the above figures, there is no evidence that syphilis plays any direct or very important part in the production of cancer.”

(1) The ”lactose+ indol+” index as employed in temperate climate is usually an adequate criterion of water purity.

(2) Where a positive test does not appear to be substantiated by the sanitary findings, a further differentiation of the organisms isolated becomes necessary. The methyl-red and citrate tests have been found to supply that differentiation in a satisfactory manner.

(3) In the Tropics, false positive “lactose-indol” tests are commonly encountered, owing to the presence in large numbers in soil and water of organisms derived from sources other than recently excreted faeces.

(4) In the Tropics, the lactose-indol test should always be confirmed by the methyl-red, citrate and saccharose tests or such other reactions or groups of reactions as may be found by a local survey to be applicable.

My very grateful thanks are due to Dr P. A. Clearkin, Deputy Director of Laboratory Service, Tanganyika Territory, for his ready advice and constant encouragement; and also to Mr W. Whitley, Analytical Chemist, who performed a chemical analysis of the water samples, and very kindly gave me the benefit of his opinion on them. In addition I have to thank Dr R. R. Scott, Medical Officer of Health, and the Staff of the Health Office, Dar-es-Salaam, who have rendered every facility in the choice and collection of samples. It is a pleasure to be able to record once more my indebtedness to Prof. Bigger, of Trinity College, Dublin, whose fund of valuable suggestions and kindly criticism has been ever at my disposal.

1. Bact. aerogenes is practically universally present, although in small numbers in the stools of normal adult humans. The stools of one individual, however, repeatedly gave negative results. The organism has also been isolated from the faeces of horse, cow, sheep, pig, dog, cat, wild rabbit, wild rat and wild mouse.

2. The use of modifications of the citrate medium, containing lithium or barium, is useful in the isolation of Bact. aerogenes when B. pyocyaneus is abundant.

3. Bact. aerogenes predominates over B. coli in soil, the contamination of which by faecal material was unlikely. The B. coli isolated from such soil do not show differences by the tests used from typical faecal strains of B. coli.

4. In the municipal water supply of Liverpool the proportion of Bact. aerogenes to B. coli is relatively high and increases on storage.

5. In water contaminated with faeces, the proportion of Bact. aerogenes to B. coli is relatively low but is rapidly reversed on storage. This is largely due to the death of the B. coli, but may in part be also due to multiplication of the Bact. aerogenes present.

6. Preponderance of Bact. aerogenes over B. coli in a water supply is indicative of either (a) contact with soil which is not contaminated with fresh faeces, or (b) long past faecal contamination.

7. Preponderance of Bact. aerogenes over B. coli in a water supply may, for practical purposes, be regarded as an indication of freedom on the part of the water from pathogenic organisms, including B. typhosus and B. paratyphosus B.

8. The repeated examination of faeces during storage showed a marked increase followed by a gradual decrease in the total number of organisms present. The decrease coincided with an increase in the numbers of Bact.aerogenes relative to the organisms present. Whether an absolute increase in the numbers of Bact. aerogenes occurred, was not determined.

9. A plea is made for uniformity among the tests adopted by future workers for the identification of coliform organisms, and an exact statement of the methods employed.

The writer desires to thank Prof. J. M. Beattie for helpful advice throughout the course of the investigation.