By the use of gastric mucin to enhance the virulence for mice of meningococcus cultures, further comparative data on stock and recently isolated strains have been secured. Marked differences in virulence occurred among both stock and recent cultures. Certain stock strains of groups I and III which have been used in the production of serum for many years were found to have retained a relatively high degree of virulence.

A larger proportion of recent strains than of stock strains proved to be highly virulent, but a number of the fresh cultures were of a low degree of virulence.

A reduction in the virulence of two stock strains as well as a loss in precipitative activity resulted from their maintenance on certain media. Thus, the type of medium was again shown to be an important factor in preserving the essential activities of strains which are to be used in the production of serum.

Polyvalent antimeningococcus serum produced with six stock strains exhibited marked protective potency against a virulent stock strain and highly virulent recent strains of groups I and III. The results of comparative tests of various routine and experimental sera indicated wide variations in protective activity.

As a gauge of the protective activity of antimeningococcus serum, the method described gives definite promise of value.

1

Presented at the meeting of the American Association of Immunologists, New York, New York, April 17, 1935.

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