Populations of Chilomonas paramecium have been maintained in a standard concentration of nutrient medium (0.1% beef-extract with 0.1% sodium acetate), at eight different temperatures, from 5 to 36° C. The temperatures 5 and 36° C. did not support the growth of a population. The rate of population growth increased with increase of temperature up to a maximum, and then decreased. The maximum yield, on the other hand, was not affected, within wide limits, by different temperatures. The relationship between temperature and maximum size of population was different when maximum size was expressed in total number of organisms from that when maximum size was expressed in terms of total volume of organisms. In the former case, the maximum size increased with the increase of temperature; while in the latter it decreased with increase of temperature.

Bělehrádek's temperature coefficient, b, of the multiplication rate of Chilomonas did not show significant differences for different temperature ranges, while the coefficients Q10, and the thermal increment µ were larger for the lower temperature range.

The size and shape of Chilomonas were found to depend on the temperature and on the age of the population. With increase in temperature, the size of organisms decreased to a minimum and then increased again, so that organisms were largest at extreme temperatures. In general, the organisms were more slender at lower than at higher temperatures. At all temperatures, the flagellate increased in size at the beginning of population growth and later decreased. Variation in size and shape was greatest at the beginning of growth and during transition to the maximum stationary phase.

Part of a dissertation presented for the degree of Doctor of Philosophy in the University of Cambridge.