Rapidly Growing Respiration-deficient Variant of Saccharomyces Cerevisiae.

medium were placed in culture tubes (16 by 150 mm). A layer of mineral oil 1 cm deep was placed on the surface of the medium, and the tubes were stoppered with cotton plugs. The tubes were then placed in an autoclave and heated for 15 min at 15 lb per in.2 During autoclaving, the culture tubes were tilted at a 200 angle to increase the exposed surface area; this reduced the problem of the medium blowing out of the tubes during cooling. The culture tubes were removed from the autoclave as soon as the pressure was down, and they were immediately placed in the modified pressure cooker shown in Fig. 1. The container was rapidly flushed with nitrogen for 5 min, followed by a slow flushing for 10 min. When the flushing was complete, a positive pressure of about 0.5 atm of nitrogen was put in the container. The tubes were allowed to cool for at least 12 hr to ensure their stabilization at room temperature. When the tubes were removed from the container, the cotton plugs were immediately replaced with sterile rubber stoppers. The tubes were stored at room temperature and used in a short time. Inoculation of the medium could be made with a loop, a needle, or small-diameter pipette. Even though the presence of the oil layer was a safeguard against oxygen entering the medium during inoculation, the tubes were not kept open any longer than was absolutely necessary. The inoculation was followed by a thorough flushing of the area above the oil with nitrogen (Fig. 2) and restoppering of the tubes as rapidly as possible. This method was adapted especially for use in determining the morphology and physiology of some strictly anaerobic cocci isolated from the small intestine of the chicken. The results of the studies indicated these cocci to be closely related to members of the genera Peptococcus and Peptostreptococcus.