GROWTH STUDIES ON CILIATES VI. DIAGNOSIS, STERILIZATION AND GROWTH CHARACTERISTICS OF PERISPIRA OVUM VIRGINIA C. DEWEY 1 AND G. W. KIDDER (Arnold Biological Laboratory, Broisni University and the Marine Biological Laboratory, Woods Hole, Mass.) The growth characteristics of a number of species of ciliates have been reported recently in the literature. Most of these papers deal with saprozoic forms (Phelps, 1935, 1936, etc.) or with bacteria-feeders (Johnson, 1933; Kidder and Stuart, 19396). The report which is to follow deals with observations of a quantitative nature made on the holotrichous ciliate, Pcrispira ovum, and represents the first attempt at an anlaysis of the growth characteristics of an obligate carnivore in bac-teria-free medium, although Brown (1940) has published a brief ac-count of some of the growth characteristics of Lcucophrys patula, a facultative carnivore. Due to the fact that Pcrispira is not a common genus and its previous descriptions have been contradictory (Stein, 1859; Levander, 1894; Kahl, 1926), a rather complete description of its organization will be given. This description will serve to establish the identity of our experimental organism and should eliminate con-fusion in future investigations, regarding its specific designation. We agree with the views expressed by Taylor and Furgason (1938) and Furgason (1940) that the space devoted to a purely morphological de-scription is warranted as a means of standardization of experimental material. MATERIAL AND METHODS During the summer of 1939 a number of specimens of Pcrispira ovum were found in a sample taken from a fresh water stream on Gif-ford St. in the town of Falmouth, Massachusetts. This sample con-tained many Euglcna along with numerous other species of protozoa. The Perispira were isolated and maintained in mass culture, along with their associated bacteria and Euglcna gracilis, for a period of two months before any attempt was made at sterilization. During this period care had to be taken to make frequent sub-cultures, as heavy bacterial growth proved to be detrimental to the Pcrispira. 1 Aided by a grant from the Manufacturers' Research Fund for Bacteriology and Protozoology at Brown University. 255
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