When the four original stock cultures were streaked on to glucose nutrient agar (GNA) and King's B glycerol agar, no bacterial growth developed on any plate incubated at 37 ° C. A blue-green Penicillium sp. grew on the GNA plate inoculated from the Tribonema culture, but all the rest were sterile. At 25 ° C a variety of bacteria, as judged by colonial appearance, grew on all plates from all four culture series. From the 25 ° C GNA plates, 12 colonies were randomly selected, characterised and identified as far as possible; these data (for 11 isolates, because one subsequently died) are presented in Tables II and III. The results concerning the properties of the micro-organisms identified from the sterility-test plates (which had been inoculated with 1-0 ml volumes of the antibiotic- treated cultures) are given in Table IV.