Further studies on trace elements and BCG cultures.
The present study verifies an earlier one in which it was shown that there is a direct relationship between the zinc content of the glycerol in the medium used for the preparation of BCG vaccine and the type of growth obtained. In the previous work zinc was added directly to the glycerol. In this report a more reliable and practical method is suggested, i.e., the storage of 96% reagent-grade glycerol in galvanized or zinc-lined tanks for periods of at least 5 months. Whereas poor sunken growths were obtained when the original glycerol was used, media made with glycerol stored in the zinc-lined tanks until its zinc content attained levels of from 5 to 10 p.p.m. yielded crisp, dry and abundant growths. There was no appreciable increase in the iron, copper or lead content of the stored glycerol.