The increase of protoplasmic bulk in unicellular organisms may be considered as made up of 2 constituent processes; first, the accretion of material by the individual, and, secondly, the reproduction of individuals. These 2 activities are well understood to be interrelated, since reproduction soon ceases when assimilation stops. The quantitative relation between these processes has been described for yeast and for Bacillus megatherium in the first 2 papers of this series (Bayne-Jones and Adolph, '32). The present study of Bacterium coli is the last of the series.
Measurements of body size in Bacterium coli are much less precise than in the other species studied. This is due to the facts that the absolute size of the individual bacillus is small, the duration of one generation is short, and the multiplication of individuals proceeds for a very brief time. Hence the absolute errors of photographing and measuring individuals lead to enormous relative errors. Calculations of growth, theref ore, give averages of significance rather than rates characteristics of individuals.
More data are available upon the physiology of Bacterium coli in artificial culture media than any other species of microorganism. It should be possible, therefore, to correlate the growth of the individual with other cultural characteristics.