Tsay's missing link was a kind of filamentous bacteria of the order Actinomycetales that resembles mold. Although there are approximately 9000 different actinomycetes on the planet, due to insufficient research, agricultural applications have only been found for three or four of them, Tsay's formula naturally being one of them.
這種由一群絲狀菌所組成、外觀類似黴菌的「放射線菌」，全球已知約有 9,000 種，但因為缺乏詳盡研究，目前被運用在農業上的只有 3 ∼ 4 種，「蔡 18 菌」即是其中一種。