ii8 GROWTH 



this limited reproduction under anaerobic conditions. This 

 absorption of oxygen, which is a linear function of time, takes 

 place with great rapidity ; thus in one instance it was found 

 that "3 gram of pressed yeast per loo c.c. of liquid completely 

 absorbed the oxygen in two and a half hours. Horace Brown 

 concludes that the power of reproduction is impressed in the 

 cell at the very outset by the absorbed oxygen and that a 

 quantitative relation exists between this absorbed oxygen and 

 the number of units which the initial yeast cell can finally 

 gemmate. The action of the oxygen is one of induction and, 

 according to Horace Brown, all the known facts can be ex- 

 plained on the assumption that the available oxygen is equally 

 divided between the initial cells and the consequent variation 

 in the oxygen charge which these cells must receive when the 

 ratio of the seed yeast to the available oxygen varies. 



The amount of oxygen in aerated wort may be very small 

 but its effect may be very great : thus I c.c. of oxygen in aerated 

 wort brings about a growth sixty times greater than the same 

 amount of oxygen in nonaerated wort* Slator is impressed 

 by the importance of carbon dioxide as a conditioning factor 

 in the growth of yeast and he considers that the influence of 

 this gas is much greater than is generally supposed, in fact 

 that some of the observed effects generally ascribed to the direct 

 influence of oxygen may be due to its indirect action in 

 lessening the supersaturation of the wort with carbon dioxide. 

 For measurements of the rate of growth in wort and in wort 

 saturated with carbon dioxide show much retardation, possibly 

 due to the carbon dioxide rather than to the lack of oxygen. 

 These measurements are confirmed by controlled experiments 

 in which the carbon dioxide was the limiting factor. In fact, 

 a correlation can be made out between the crop of cells and 

 the concentration of carbon dioxide in the medium : 



Proportionate Concentration Crop of Crop 



of Carbon Dioxide = a. Cells, t a 



1-08 3*0 2-8 



i -08 3'o 2-8 



1-46 4-1 2-8 



1-48 4*5 3'i 



2'i3 6'i 2*9 



2-33 6-5 2-8 



* Slator: " Journ. Chem. Soc.," Lond., 1921, 119, 115. 

 fUnit of crop of cells = 7*65 x io 6 cells per c.c. 



