Histoplasmin potency as affected by culture age

A long term controlled study of histoplasmin production by 4 isolates of Histoplasma capsulatum showed a wide variation in time required for skin test antigen production. There appeared to be no specific time for harvesting cultures of H. capsulatum to produce an histoplasmin that would give a standard skin test on homologously infected guinea pigs. Concurrent chemical studies on the culture filtrates indicated, however, that skin test activity may be related to chemical changes in the medium. These studies indicated a close relationship between increasing skin test potency and increasing total protein with decreasing total carbohydrate.