128 YEAST iv 



and, on the other hand, by the Thenardian doc- 

 trine, supported by Pasteur, according to which 

 the yeast plant assimilates part of the sugar, and, 

 in so doing, disturbs the rest, and determines its 

 resolution into the products of fermentation. Per- 

 haps the two views are not so much opposed as 

 they seem at first sight to be. 



But the interest which attaches to the influence 

 of the yeast plants upon the medium in which 

 they live and grow does not arise solely from its 

 bearing upon the theory of fermentation. So long 

 ago as 1838, Turpin compared the Torulce to the 

 ultimate elements of the tissues of animals and 

 plants " Les organes elementaires de leurs tissus, 

 comparables aux petits v<5gtaux des levures 

 ordinaires, sont aussi les decompositeurs des sub- 

 stances qui les environnent." 



Almost at the same time, and, probably, equally 

 guided by his study of yeast, Schwann was en- 

 gaged in those remarkable investigations into the 

 form and development of the ultimate structural 

 elements of the tissues of animals, which led him 

 to recognise their fundamental identity with the 

 ultimate structural elements of vegetable organ- 

 isms. 



The yeast plant is a mere sac, or " cell," con- 

 taining a semi-fluid matter, and Schwann's micro- 

 scopic analysis resolved all living organisms, in the 

 long run, into an aggregation of such sacs or cells, 

 variously modified ; and tended to show, that all, 



