Reported attack rates from different batches of icterogenic serum-containing material administered parenterally vary considerably one from another, as shown in Table 1. These data were selected because they represent essentially complete follow-up studies on all known individuals receiving units of icterogenic substances from the common lots indicated.
Specificity of Attack Rates
Are the above differences in attack rates due more to volume of icterogenic material administered than to concentration of virus particles (assuming no difference in the qualitative capacity of a viable virus particle to infect), or is there a wide variation in the natural or acquired immunity (or both) in an otherwise fairly homogeneous healthy population? The only existing body of data large enough to be usefully applied to these questions is contained in the carefully prepared follow-up studies of Sawyer et al. (1944) on the outbreaks of serum hepatitis following the administration of 2 batches of the serum-containing