Simple agglutination tests divided into two main groups a series of 34 meningococci obtained from the cerebro-spinal fluid of cases of meningitis during the recent epidemic.

Certain of these strains of meningococci, which were either not agglutinated or only slightly by any of the sera employed, could be placed in one or other of the groups by the demonstration of their agglutinogenic capacity.

Certain individual strains in each of the groups were agglutinated to a less degree than the homologous strain, and certain strains were agglutinated by sera of both groups.

For further evidence as to specific relationship resort was made to agglutinin absorption experiments.

While the question, as to whether meningococci can be divided into independent groups by means of agglutinin absorption tests, must, at this stage of the investigation, remain open, the experiments detailed above indicate that variations in absorptive capacity between individual strains of meningococci are analogous to, though not in actual correspondence with, variations in agglutinability.

The non-contact naso-pharyngeal strains, culturally identical with meningococci, exhibited in relation to monovalent agglutinating sera prepared with cerebro-spinal meningococci, the same tendency to grouping as the cerebro-spinal strains and similar variations in agglutinability. The 28 non-contact strains, which have been investigated serologically, reacted to the following extent with one or other of the above-mentioned meningococcus immune sera:—5 showed complete agglutination in 1:400 or over, 10 in 1:200 or over, 6 in 1:100; 7 were not completely agglutinated in dilutions higher than 1:50. The first-mentioned 5 absorbed, from the respective agglutinating sera, the agglutinins for the homologous strains. From one of these 5, N.P. 10, a serum was prepared which was found to agglutinate strains in Group II. Of the 16 strains which agglutinated with meningococeus sera between 1:100 and 1:400, a few were tested as to their absorptive capacity in relation to two sera and, as will be seen from the absorption tables, showed evidence of agglutinin absorption. The absorption, though slight in amount, was equal to that occurring with the same sera treated with certain cerebro-spinal strains. The remaining 7 strains, which were agglutinated feebly by the meningococeus sera employed, are being subjected to further investigation (1) as to their agglutinability in relation to other cerebro-spinal meningococeus sera, (2) as to their capacity for producing agglutinating sera for cerebro-spinal meningococci. Taken as a whole, the serological results afford indication of a division of meningococci into two groups with some overlapping of each.

The theoretical explanation may be that the antigenic substance of the meningococeus contains one or other of two specific components, A and B, and sometimes contains both components, one of the two then being present in greater amount than the other. Consequently some strains produce sera with agglutinins of the A class alone; others create agglutinins of the B class alone; others produce both A and B agglutinins, with preponderance in some cases of A and in other cases of B. As regards agglutinability, again, some strains are capable of combining with A alone, others with B alone, and others with both A and B, but to a greater degree with the one than with the other.

Comparing the capacity of an individual strain for producing agglutinin with its capacity for combining with agglutinin, I find that in some cases these two capacities appear to coincide. But this is not a general rule. For example, a strain may have limited capacity for combining with agglutinin, but much greater capacity for producing agglutinin; again, it may combine with A alone, or mainly with A, but produce agglutinins in which B preponderates over A.

Absorption experiments, again, show that whilst there is sometimes a correspondence between capacity to absorb and capacity to create, or combine with, specific agglutinin, this correspondence is not a general rule.

These last two considerations show that the characteristics of different strains of meningococci, while affording a basis for division into groups, are closely inter-related, and, in fact, are connected by inseparable links, which appear to make it impossible to effect a definite cleavage between the one group and the other.

The above observations have been suggested by the results so far obtained, but further work on this subject is in progress, with special reference to the identification of the meningococcus in the naso-pharynx.