234 PHYSIOLOGY OF BACTERIA 



by the yeast. The final concentration in normal wort 

 was 3.6% alcohol. 



Special experiments demonstrated that no other 

 volatile or non-volatile fermentation products were 

 the cause of growth inhibition. Good aeration, however, 

 increased the final crop considerably, and it seems cer- 

 tain that the first limiting factor of yeast growth in 

 wort is lack of oxygen which is nothing else than lack of 

 food. Another example where lack of food is the cause of 

 cessation of growth will be shown on p. 248. It concerns 

 the growth of Micr. pyogenes in a meat infusion medium. 



Aside from these two factors, accumulation of fermen- 

 tation products, and exhaustion of food supply (includ- 

 ing oxygen as a food), a third possibility has been 

 repeatedly claimed, and has been disclaimed as often 

 by others ; namely, the existence of a more or less specific 

 cell excretion which is thermolabile and of colloidal 

 nature. Eijkman (1905) claimed such a compound for 

 Bad. coll. Full-grown gelatin cultures, after steam 

 heating, allowed normal growth to occur again while 

 the same gelatin, remelted without heating to high 

 temperatures, showed no growth upon re-inoculation. 

 This experiment was modified in various ways, always 

 with the same result. Conradi and Kurpjuweit (1905) 

 enlarged upon this theory. Later authors (e.g., 

 Manteuffel, 1907) disproved this by the claim that the 

 absence of growth was merely due to lack of food. 

 Wherever large numbers of living cells were left, the 

 food was divided between so many cells that none could 

 multiply visibly. If, however, heat destroyed the old 

 cells, the newly inoculated cells had sufficient food for 

 growth (see also Henrici, 1928). 



Rahn (1906) observed with Ps. fluorescens that new 

 growth developed in old cultures upon re-inoculation after 



