Abstract
Pantothenic acid, a growth-promoting substance of universal occurrence, was tested for its effect on the growth of two remotely related protozoan forms, namely, Colpidium striatum and Hæmatococcus pluvalis. The tests were conducted over a wide pH range. In the case of C. striatum a doubling of the growth occurred in the pantothenic acid cultures on the acid side of neutrality (pH 5.5-6.6) while no acceleration was observed above pH 7.0. With Hæmatococcus pluvialis no differences were noted in the test and the control tubes. It was shown further that pantothenic acid was not the substance lacking in certain incomplete proteins(zein, gliadin, and gelatin) which failed to support indefinite growth of C. striatum.