12 PHYSIOLOGY OF BACTERIA 



that, so far, endogenous catabolism has been studied 

 only in yeasts. 



As early as 1803, Thenard observed that yeast fer- 

 menting in pure sugar solutions loses protein. Yeast 

 may lose 30% or more of its nitrogen, and finally loses 

 the ability of rapid fermentation (Schiitzenberger, 1876). 

 Pasteur and many others have observed a decrease of 

 nitrogen in yeast, but few of these experiments have 

 been made quantitatively. 



Though endogenous catabolism of yeast is more rapid 

 than with higher organisms, autolysis is still swifter. 

 Rubner (1904) observed in living yeast kept in a 20% 

 sugar solution, a loss of nitrogen of 58% in six days, 

 while the same yeast suspended in water + toluol, i.e. 

 after being killed, lost 90% of its nitrogen in four days. 

 Effront (quoted from Euler-Lindner) found that 500 

 gm. yeast in distilled water lost 39 mg. of nitrogen in 

 twenty-four hours while the same yeast in water -|- 

 alcohol + hydrofluoric acid lost 72 mg. After five days, 

 the latter liquid, from the dead yeast, contained ten 

 times as much nitrogen as the liquid from the living yeast. 



Rubner (1913) made extensive experiments on the 

 nitrogen catabolism of fermenting yeast cells; the main 

 results are given in Table 1. The first two experiments 

 refer to yeast kept in 20% sugar solution at 38°C. for 

 three and six days. Different yeast was used in these 

 two experiments. For the third experiment, the yeast 

 remained in a 10% sugar solution at 28°C. for twenty- 

 four hours, was then centrifuged out, and suspended in 

 new sugar solution; after another twenty-four hours, the 

 sugar solution was renewed in the same way, and this 

 was repeated five times. 



In connection with the last experiment, it will be of 

 interest to know that the total quantities of alcohol 



