1. In two areas in the Eastern Counties, Cambridge and Norwich, naso-pharyngeal swabs were taken from 400 individuals, who represented different conditions of health and social circumstances.

The investigation was made at Cambridge between the months of June and October, 1916, and at Norwich during August, 1916.

Owing to the low incidence of cerebro-spinal fever in the two towns during the year 1916 (see p. 249), the general population may be regarded as practically “non-contact” in respect of this disease.

2. As a result of the investigation, strains giving all the cultural and microscopical tests of the meningococcus were obtained as follows:

(a) From 200 swabs taken at Addenbrooke's Hospital during June and July, 1917, mostly from normal people, 30 strains.

(b) From 100 swabs taken at the Norfolk and Norwich Hospital during August, from individuals mostly in impaired health, 27 strains.

(c) From 100 swabs taken in Cambridge during October, from factory employees, who were all in good health and mostly in comfortable circumstances, 37 strains.

3. Such strains were found more often in males of every age group than in females, and in adults more often than in children.

In regard to the influence of health and surroundings, the results of the investigation grouped together show a larger proportion amongst town dwellers than amongst country people and amongst people with impaired health than amongst the healthy.

General conclusions cannot, however, be drawn from these figures because conditions were not always comparable. For instance, the majority of country people were examined in June and July, when positive findings were low.

In examining the employees at a factory, I obtained the strains in a higher proportion from the men working in those shops where air space was more restricted and ventilation less perfectly effected.

4. The 94 strains collected from 400 naso-pharyngeal swabs were tested as regards their agglutinability against certain monovalent sera. These sera were prepared from seven strains of meningococci of cerebrospinal orgin, and from two of the naso-pharyngeal cocci which had been isolated during the course of the investigation. The meningococcal strains used for preparing the sera included strains which had been found identical with others occurring with considerable frequency in cerebrospinal fluid and capable of being grouped in two main groups; they also included strains which differed from these and were apparently rarer; but there is no reason to assume that every variety occurring in the specific disease was represented.

The results of the tests on the above 94 strains may be classified as follows:

(a) 22 gave no agglutination above 1: 100 with any of the sera used.

(b) Two agglutinated well with certain sera, but also agglutinated with normal rabbit serum.

(c) 31 agglutinated up to 1–200 or 1–400 with the sera of a certain group (M I–M IV), and in some instances gave similar agglutination with other sera not belonging to this group.

(d) 39 agglutinated with the sera of the group M I–M IV to the full titre of the homologous strains, while with the sera belonging to other groups good agglutination was not often obtained.

This last group of 39 strains (41 per cent. of all tested) appears to be indistinguishable by simple agglutination tests from the M I–M IV group of cerebro-spinal meningococci. The previous group of 31 (33 per cent. of all tested) shows evidence of serological relationship with meningococci of cerebro-spinal origin, but it is not possible on their agglutination tests alone to give an opinion as to their identity with any meningococcal group.

Agglutination tests as a whole indicated that about 74 per cent. of strains collected on account of their resemblance to the meningococcus in culture, gave evidence of relationship to the meningococcus in virtue of their agglutination reactions with anti-meningococcal sera.

5. In order to determine if the absorption test would corroborate the relationship shown by agglutination, absorption tests were done against a serum prepared by inoculation of a cerebro-spinal strain of meningococcus, M I, with all the strains, culturally and by simple agglutination indistinguishable from pathogenic meningococci, which had been collected from the last 100 swabs (normal factory employees, Cambridge). Nine absorbed the agglutinin as well as the homologous coccus and four absorbed it partially.

Therefore, out of 100 normal people who had not been in contact with a case of cerebro-spinal fever, 9 per cent. were shown to be harbouring organisms in their naso-pharynx which were serologically identical with meningococci of pathological origin (cerebro-spinal fluid) and, in addition, 4 per cent., making 13 per cent. in all, were so closely allied as to be doubtfully distinguishable even by the test for absorption of agglutinin.

Similar results were obtained with strains obtained from Norwich.

The above results were confirmed by testing absorption by these cocci from another serum prepared with another spinal strain of meningococcus possessing properties almost identical with M I. I have not investigated absorption with sera prepared with strains which differ serologically from M I.

6. With regard to those naso-pharyngeal strains which were not identified with cerebro-spinal strains by serological tests (agglutination and absorption), I consider that in view of the great variation in the serological reactions shown by different strains of undoubted meningococci and even by different emulsions of the same strain, it is very difficult, if not impossible, to exclude any such microscopically and culturally typical organisms from the meningococcus group on the basis of serological tests.