HANSEN'S EXPERIMENTS WITH YEAST. 269 



the most favourable circumstances. The race improvement in 

 such cases consists in a repeated selection of the best individuals ; 

 but the results of the experiments made by Hansen and others 

 in this direction show that it is impossible to lay down any 

 definite rules, tentative experiments being essential. In some 

 cases disappointment will follow, the results failing to come out 

 as desired, owing to uncontrollable circumstances. The matter is 

 entirely different from the mere production of asporogenic races 

 and the like, where the conditions are known and under control. 

 Finally, it must be borne in mind that when the material for the 

 experiments in race improvement are taking from the contents of 

 the fermentation vessel in the brewery, one cannot be certain that 

 any genetic connection exists between the race so taken and the 

 original pitching yeast, for they are not necessarily descended 

 from one and the same ancestor even though exhibiting the same 

 botanical characteristics. 



Similar communications on race improvements have also been 

 published in connection with wine yeasts, though again without 

 any definite statement of method ; and indeed some of these 

 reports, from practical sources, even fail to mention the species of 

 yeast originally employed. 



