1. In the course of the examination of sputum from cases of lobar pneumonia, observations have been made on the incidence of the chief types of pneumococci. In the district from which the material was obtained, there was an apparent local diminution in the number of cases of lobar pneumonia due to Type II the figures were 326 per cent. of Type II cases in the period 1920–22, and only 74 per cent. in the period 1924–27. The incidence of Type I was approximately the same in the two periods, the percentages being 3O6 and 343.

2. Several different serological varieties of pneumococci have been obtained from the sputum of each of several cases of pneumonia examined at various stages of the disease. This has occurred most frequently in cases of pneumonia due to Type I, and in two instances four different types of Group IV were found in addition to the chief types. The recovery of different types is facilitated by the inoculation of the sputum (preserved in the refrigerator), together with protective sera corresponding to the various types in the order of their appearance.

3. Two interesting strains of Group IV pneumococci have been obtained from pneumonic sputnm.

One was an R strain which produced typical rough colonies, yet preserved its virnlence for mice and its capacity to form soluble substance. This R pneumococcus developed a large capsnle in the mice, which died of a chronic type of septicaemia. A strain producing smooth colonies was obtained from it in the course of a prolonged series of passage experiments.

The second strain, which was proved not to be a mixture, agglutinated specifically with the sera of two different types. In the peritoneal cavity of the mouse the specific soluble substance of each type was produced.

4. A method of producing the S to R change through ageing of colonies on chocolate blood medium containing horse serum is described. After two to three days' incubation small rough patches appear in the margins of the smooth colonies, and from these pure R strains can be isolated.

5. It has been shown that the R change is not equally advanced in the descendants of virulent pneumococci which have been exposed to the action of homologous immune serum. Some R strains form traces of soluble substance in the peritoneal cavity of the mouse; these revert readily to the virulent S form and, in addition, are able to produce active immunity. Others show no evidence of S antigen; spontaneous reveraion takes place with difficulty, if at all, and they are incapable of producing active immunity. The stronger the immune serum used, the more permanent and complete is the change to the R form.

6. Restoration of virulence to an attenuated R strain, with recovery of the S form of colony and of the original serological type characters may be obtained by passage through mice. The change from the R to the S form is favoured by the inoculation of the R culture in large doses into the subcutaneous tissues; but the most certain method of procuring reversion is by the inoculation of the R culture, subcutaneously into a mouse, together with a large dose of virulent culture of the same type killed by heat. Incubation of such a mixture in vitro does not induce reversion.

7. Reversion of an R strain to its S form may occasionally be brought about by the simultaneous inoculation of virulent culture of another type, especially when this has been heated for only a short period to 60° 0., e.g. R Type II to its S form when inoculated with heated Type I culture.

8. Type I antigen appears to be more sensitive to exposure to heat than Type II antigen, since the former loses the power to cause reversion when heated to 80° C., whereas Type II culture remains effective even after steaming at 100°C.

9. The antigens of certain Group IV strains appear to be closely related to that of Type II, and are equally resistant to heat. Steamed cultures of these Group IV strains cause the R form derived from Type II to revert to its S form, while they fail to produce reversion of the R form derived from Type I.

10. The inoculation into the subcutaneous tissues of mice of an attenuated R strain derived from one type, together with a large dose of virulent culture of another type killed by heating to 60° C., has resulted in the formation of a virulent S pneumococcus of the same type as that of the heated culture.

Thp newly formed S strain may remain localised at the seat of inoculation, or it may disseminate and cause fatal septicaemia.

The S form of Type I has been produced from the R form of Type II, and the R form of Type I has been transformed into the S form of Type II.

The clear mucinous colonies of Type III have been derived both from the R form of Type I and from the R form of Type II, though they appear to be produced more readily from the latter. The newly formed strains of Type III have been of relatively low virulence, and have frequently remained localised at the subcutaneous seat of inoculation.

Virulent strains of Types I and TI have been obtained from an R strain of Group IV.

11. Heated R cultures injected in large doses, together with small doses of living R culture have never caused transformation of type, and only rarely produced a reversion of the R form of Type II to its virulent S form.

12. The results of the experiments on enhancement of virulence and on transformation of type are discussed and their significance in regard to questions of epidemiology is indicated.

(1) Fifty S. aureus and 30 S. albus strains obtained from infective processes in man have been investigated. Such cultural reactions as were completed did not differentiate between strains of S. albus and S. aureus, or serve to group these cocci; we found, however, that 94 per cent, of the S. aureus strains fermented mannite, as opposed to 40 per cent, of the S. albus strains. These results are in accordance with the findings of Cummins and Cumming (1913) and Hine (1922).

(2) A close degree of correlation between pathogenicity for rabbits, pigment formation, and biochemical activity was noticed among the S. aureus strains. Out of 19 pathogenic strains of S. aureus, 9 showed medium pigmentation and 10 were strongly pigmented.

(3) Anti-sera were prepared by inoculating rabbits with living cultures, 24 hours old, of the various strains. The S. aureus rabbits and a few of the S. albus received two preliminary doses of the specific vaccine, but little or no protective action was afforded from the doses of living cocci injected.

(4) Nineteen out of 25 cultures of S. aureus killed rabbits, but only 3 out of 18 cultures of S. albus.

(5) Fifteen strains of S. aureus and 15 of S. albus were used for the preparation of anti-sera, and tested against as many antigens as possible, by the methods described by Dudgeon and Bamforth.

(6) Cultures of S. aureus produced efficient anti-sera more readily than S. albus cultures, but when an active S. albus anti-serum was produced, it appeared to be as effective as the S. aureus anti-sera.

(7) A marked difference in efficiency between S. aureus and S. albus antigens was noted. S. aureus antigens were almost three times more active than S. albus antigens.

(8) Pathogenic strains of S. aureus and S. albus produced more efficient precipitin antigens than non-pathogenic.

(9) From the microscopical examination of the deposit formed in the precipitin reactions, a difference was noted between S. aureus and S. albus antigens.

(10) The study of the precipitin reactions has failed to show any hard and fast dividing line between staphylococci of different colours, or of different cultural reactions. We are inclined to agree with Winslow, Rothberg and Parsons (1920) and with Dudgeon's original view in 1908, that the pyogenic, Gram-positive staphylococci must be regarded as members of one common family.

In both of these diseases, locomotor ataxia and general paralysis of the insane, the necessary antecedent is now generally recognised as syphilitic infection. Whether these two types of nervous degeneration occur at random in those so predisposed to their development, or whether some underlying factors at present unknown or only suspected operate selectively is a problem of some importance.

The subjection of the scrotum of the dog for 10 minutes daily for 28 days to a stream of water at 39·5 40·0° C. does not materially affect the testes. It is unlikely that ordinary hot bathing affects male fecundity.

The possibility that the prevalence of diseases in which there is no specific causal organism may be affected by the prevalence of other diseasses of a contagious nature is well recognised. Even in the early days of bactriology interrelationships between infectious diseases and puerperal septicaemia were suspected on purely statistical grounds. Longstaff (1891), for example, pointed out the remarkably close correlation between the seasonal variations and the secular trends of the mortalities of erysipelas and childbed fever—a relationship so close that he “found it difficult to avoid the conclusion that they were both due to the one poison.” A somewhat similar but less striking association was shown with other inflammatory diseases, such as pyaemia, scarlet fever, “rheumatism of the heart or pericardium” and diphtheria. Even more emphatic were the views of Minor (quoted by Longstaff) who, with reference to the association between erysipelas and puerperal fever, gave reasons for the belief that there existed an intimate connection between them, and that “in any place where erysipelas is found, there will be found puerperal fever.”

Drinking water has long been supposed to play an important part in the causation of endemic goitre. Estimations by v. Fellenberg (1923, 1924) in Switzerland and by Mcclendon and Hathaway (1924) in the United States have shown that, in these countries, drinking water in goitre areas contains less iodine than in goitre-free areas. The iodine content of several waters has been estimated at this Institute. The results show that in this country there is no correlation between presence of goitre and a low iodine content in drinking water. It is true that the lowest figure (Swindon) is for water from a goitre area, but the next one (Aberdeen) is not. The figures for Cumberland and Derbyshire, both goitre areas, are not low.

The difficulties encountered in distinguishing pneumococci from streptococci, particularly S. salivarius, have been enumerated and the morphological and cultural similarities between the two groups of organisms have been pointed out. If bile-solubility is taken as the distinguishing mark of a pneumo-coccus it will be found that there are a large number of bile-insoluble streptococci commonly met with in the respiratory tract and sometimes playing an important part in disease, which bear very strong resemblances to pneumococci both in shape, colony, and broth culture. The similarities are specially confusing in mixed cultures on agar plates and a number of the routine tests applied quite failed to distinguish them. There naturally follows the corollary that some of these tests fall wide of the mark, and they should therefore be left out of the bacteriologist's armamentarium when the identification of pneumococci is under consideration. Morphological and cultural properties are insufficient guides to species, while the same is true of the widely recommended tests of inulin fermentation and capsule formation. Not only do some pneumococci fail to ferment inulin, but so many strains of S. salivarius show active inulin fermentation that, in the present series of organisms taken at random, the incidence of inulin fermenters amongst S. salivarius is actually higher than amongst pneumococci. Capsules were found in all the strains of streptococci in which they were sought and in all the pneumococci investigated, so that encapsulation may be regarded as a property common to members of both species.

This experiment has demonstrated that it is possible consistently to produce milk containing small numbers of bacteria and of good keeping quality by the use of milking machines.

It has been shown that the milking units and their rubber components may be successfully sterilised by steam.

The pipe lines have been shown to be a possible source of heavy contamination, and means of preventing this have been described.