The use of procaine hydrochloride in the preparation of rotifer samples for counting

Summary

Soft-bodied rotifer species often contract violently on contact with formalin and become difficult or impossible to count. Experiments have shown that this problem can be overcome by narcotizing the animals with procaine hydrochloride (PCH) before formalin is added. The method is described with particular reference to the illoricate rotifer Synchaeta kitina ROUSSELET. At concentrations above 3% PCH these animals reacted as violently to the anaesthetic as to the formalin. However, at 0.04% PCH the animals died in their extended form in about 16 hours. This concentration was tested for routine use and found to be both effective and economically acceptable. In general, the method had no significant effect on population estimates.