276 MICRO-ORGANISMS AND FERMENTATION. 



One result of HANSEN'S epoch-making discoveries has been 

 .the establishment of special laboratories, the object of which 

 is to prepare absolutely pure material for employment in 

 practice, to carry out control analyses, and to instruct 

 the younger generation in the true understanding and the 

 proper application of his discoveries. Such institutions have 

 now been established in almost all countries, and are partly 

 private and partly supported by the State ; they have already 

 produced a number of able teachers, analysts, and technologists, 

 who are working with energy and judgment to propagate more 

 widely, in science and practice, the views of the Danish 



investigator. 



HANSEN'S work has exercised an indirect influence on dairy 

 methods ; as mentioned in a previous chapter, pure cultures of 

 lactic-acid bacteria have been successfully employed on a large 

 scale for the souring of cream. Finally, also, in the tobacco 

 fermentation, SCHLOESING and SUCHLAND have experimented 

 with the view of producing a definite aroma in tobacco leaves 

 by the addition, during the fermentation, of pure cultures of 

 certain species of bacteria. 



The idea which underlies all these efforts at reform is the 

 principle which has been recognised and carried out for cen- 

 turies in horticulture and agriculture, namely, that in order to 

 obtain the desired species of plant its seed should be sown 

 free from the seed of all other plants. 



