232 CULTIVATION AND REPRODUCTION OF YEAST. 



oxygen, cannot yet be finally settled. J. BEUKEXS (VI11.) 

 reports that he found a comparatively large number of anaerobic 

 yeasts on hop cones, and TRAUBE (II.) had previously stated that 

 yeast reproduction may proceed, in certain circumstances, in the 

 absence of oxygen. On the other hand. BREFELD (XIII.) con- 

 sidered he had proved the absolute necessity for the presence of 

 oxygen. 0. KORFF (I.) observed a considerable degree of repro- 

 duction in cultures in yeast water treated with 10 per cent, of 

 saccharose and traversed uninterruptedly by a ciment of hydrogen. 

 the yeast sowing employed having been grown under similar 

 conditions. At the end of fourteen days the amount of crop 

 obtained per original cell was: San/ yeast, 876 cells; Frohberg 

 yeast, 1346 cells; and Logos yeast. 1160 cell>. According to P. 

 BARKER (I.) a Scuxharomt/ce^ isolated from ginger exhibited no 

 signs of incipient growth when oxygen was completely excluded. 



The more closely we criticise the reliability of the methods and 

 appliances hitherto used for obtaining really anaerobic conditions 

 in cultures, the smaller the trust we place in the results of the 

 experiments made in this connection, and the greater becomes the 

 doubt whether this or that anaerobic is one in the strict sense of 

 the term or merely an aerobe requiring only a very small quantity 

 of oxygen. We need only remember how difficult it is to com- 

 pletely eliminate oxygen from the gas (hydrogen, nitrogen, or 

 carbon dioxide) employed to displace the air and traverse the 

 cultures ; and the non-fulfilment of this preliminary condition 

 will certainly influence the results when we are dealing with 

 organisms that are very sensitive toward oxygen and are stimu- 

 lated by very small quantities of that gas. Now yeast is an 

 organism of this kind, being, as BREFELD (XIII.) observed, 

 satisfied with a tension corresponding to the presence of i part 

 of oxygen in 6000 parts of carbon dioxide. Traube's counter- 

 proof with the assistance of sulphindigotic acid cannot be accepted 

 unconditionally ; and the fact that yeasts will reproduce during 

 the temporary exclusion of oxygen is insufficient as proof, since in 

 such cases the yeasts consume the previously accumulated store of 

 that element. Moreover, cultures in which the vessel is provided 

 with a seal of dilute sulphuric acid during fermentation cannot 

 be regarded as having developed in the absence of oxygen. E. C. 

 HAXSEN (XXXII.) states briefly that budding occurred in his 

 experiments with nitrogen freed from oxygen ; but there is a 

 decided ditterence between this and sporulation, which takes 

 place only in presence of an abundant supply of oxygen. 



As a matter of fact, the growth and reproduction of all the 

 yeasts hitherto examined proceed more freely in aerated cultures. 

 The first results that can be classed as reliable (because obtained 

 with the counting cell) were obtained in 1879 by E. C. 

 HANSEX (XXX.), who showed that a certain beer yeast when 

 grown in wort at I2-I4 C. increased n. 2-fold in 60 hours 



