

THE AUTOFERMENTATION OF YEAST. 547 



Jodlbauer in this connection, it must be admitted that this method 

 should only be resorted to when all other means have failed. The 

 apparatus must be put together with great care in order to prevent, 

 on the one hand, any escape of fermentation carbon dioxide 

 throughout the whole of the experiment lasting about twenty 

 hours in presence of glucose, and twice as long in the case of 

 saccharose and, on the other, to exclude atmospheric carbon 

 dioxide. 



These particulars should also be borne in mind by those who 

 wish to determine the amount of sugar in urine by the fermenta- 

 tion method. More precise information on the method employed 

 for this purpose and the Einliorn saccharometer which is similar 

 to the fermentation flask noticed on p. 207 of vol. i. may be found 

 in the handbooks onUrine Analysis, especially that of Neubauer and 

 Vogel, the last three editions of which have been supervised by 

 H. HUPPERT (I.). All these handbooks advise a check experiment, 

 to ascertain the amount of carbon dioxide liberated by the yeast 

 on digestion with water only. Though the question of auto- 

 fermentation is thus touched upon, the prescriptions given leave 

 much to be desired on the score of accurracy, and in particular 

 fail to bear in mind the possible occurrence of glycogen in the 

 yeast. Excellent service in this connection has been rendered by 

 E. BticiiNER and S. MITSCHERLICH (I.) by the elaboration of a 

 method of preparing yeast free from glycogen. Utilising the 

 observations of HENNEBERG (IV.), they treated yeast by spreading 

 the pressed and screened material in a thin layer exposed to the 

 air. On the yeast being kept in the ice-chest (at about 2 C.), no 

 glycogen can be found after about a day ; at about 20 C. it dis- 

 appears in eight hours ; and as quickly as 3-4 hours in the thermo- 

 stat at 35-45 C. As a rule the fermentative power of the yeast 

 is unimpaired by this treatment. These workers state positively 

 that yeast as free as possible from glycogen must be used for the 

 detection of sugar in urine, since yeasts that are rich in glycogen 

 may give rise to the erroneous impression that the urine under 

 examination contains sugar. The permanent yeast sold under the 

 name "zymin" is not suitable for this purpose, inasmuch as it 

 contains glycogen (see p. 474, vol. ii,). 



In conclusion it may be mentioned that the value of many of 

 the scientific treatises dealing with the attenuation powers of 

 yeast will assume a different proportion when examined with a 

 view to ascertaining whether the possibility of the intervention of 

 autofermentation has been duly considered by the authors. All 

 experiments in which increased quantities of yeast have been 

 employed in one and the same test require to be repeated and 

 confirmed in this connection. 



