inoculum

inoculum (countable and uncountable, plural inoculums or inocula)

1. The active material used in an inoculation; an inoculant
   • 2015, C. Michele Thompson, Vietnamese Traditional Medicine: A Social History, page 82:

     Observers noted that Chinese variolators in Vietnam exhibited one or two slight variations in their practice, however, one constant factor is that they all introduced inoculum into the nasal passages.

• preinoculum