The high variability in infectivity of Diplococcus intracellularis makes it impracticable to standardize the antimeningitis serum on the basis of the virulence of the diplococcus.
The irregularity of reaction of small animals to the poison or endotoxin of Diplococcus intracellularis makes it impracticable to standardize the antimeningitis serum on the basis of endotoxic value.
The want of uniformity in the complement-binding power of the antimeningitis serum, and the absence of established relation between complement-binding power and therapeutic activity make the employment of this method of standardization impracticable.
The part taken by specific opsonins in promoting recovery from infection with Diplococcus intracellularis suggests their employment as a measure of the therapeutic activity of the antiserum. Methods of quantitative estimation of opsonic content of the antimeningitis serum being available, it would seem advantageous to adopt for the present as a standard of value a definite and suitable strength in opsonins of the antimeningitis serum.
As a definite and suitable standard of strength a minimum dilution activity of a 1 to 5,000 dilution of the antiserum is proposed.
Since the immune opsonins of the antimeningitis serum appear to be highly durable under proper conditions of refrigeration of the antiserum, the test proposed will be applicable when the antimeningitis serum shall have become an article of commerce.