398 PHYSIOLOGY OF BACTERIA 



Volume of 50,000,000 cells in 1 c.c. of liquid = 6 mm.^ = 0.6% of 

 volume of medium. 



All these dimensions are summarized in Table 132 

 which shows plainly that we cannot generalize from 

 yeasts to bacteria, or from bacteria to bacteriophage. 



The weights, volumina and surfaces of mold mycelium 

 are again on a different order of magnitude, but the 

 variation is so great and their mode of growth so different 

 that no general statements can be made. 



II. MULTIPLICATION OF BACTERIA 



Geometrical Progression: Bacteria divide by fission 

 into two equal cells; the successive generations, 2; 4; 

 8; 16; etc., can be described by the geometrical progres- 

 sion 21; 22; 2^; 2^ etc. 



If one cell is placed in a nutrient solution and multiplies, 

 all cells deriving from this one cell will be of the same age, 

 for there is no old cell left when the two young cells have 

 been formed. Each new set of cells is called a new 

 generation. 



If a cells are transferred to a new medium, the multipli- 

 cation follows the order a;2a;2^a;2^a; . . . 2''a; 



This rule holds true only for organisms which divide 

 by fission; it is not really accurate with yeasts. There, 

 we have a budding process with the old cell plainly 

 distinguishable from the daughter cells, even if the bud- 

 ding has gone through several generations. Thus, 

 the yeast cells in a fermenting liquid are not all of the 

 same age, and old cells may not bud as freely as the 

 younger ones. Ordinarily, the multiplication will, even 

 in yeasts, follow nearly the progression 2^; but it is never 

 safe to rely upon it. 



Generation time: The time required by one cell to 

 divide completely in two new cells is called generation 



