142 Regulation of Size in Unicellular Organisms 



Yeasts. In yeast the sizes of individuals were found 

 by Richards ('28b) to diminish progressively during 

 the early history of a culture fluid, just as was the case 

 in Scenedesmus. Later the size slowly increased to 

 a level which was maintained for several days. 



12 18 24 30 36 



Age of culture in hours 



Figure 46. Progression of body length in Bacterium coli after implanta- 

 tion on fresh agar. Volumes are calculated at / X b 2 , in which b was derived 

 from area divided by length. (Data of Henrici, '23). 



Bacteria. Only recently have changes of size with 

 age of culture been studied in bacteria. Whereas a 

 culture of ciliates or algae may require a week or two 

 to lead to significant changes of size, the heavy inocula 

 customarily used in bacterial cultures, together with 

 faster metabolism and multiplication, lead to critical 

 changes within a few hours. Observations were made 

 upon a number of different species by Clark and Ruehl 



