Liquid nitrogen storage of Anaplasma marginale complement-fixation antigen by a multiple small aliquot technique.

Anaplasma marginale complement fixation test antigens were frozen as drops in liquid nitrogen using an easily constructed apparatus. Economy in the use of antigen was achieved as the frozen drops were retrieved from storage in any required volume. The potency of the antigen was unaffected by the freezing and thawing technique. The technique is useful for storing other biological reagents.