130 YEAST IV 



of a controlling apparatus, such as a nervous system, 

 this conception ceased to be tenable. The cell 

 lives for its own sake, as well as for the sake of 

 the whole organism ; and the cells ivhich float in 

 the blood, live at its expense, and profoundly 

 modify it, are almost as much independent organ- 

 isms as the Torulce which float in beer-wort. 



Schwann burdened his enunciation of the " cell 

 theory" with two false suppositions; the one, 

 that the structures he called " nucleus " ^ and " cell- 

 wall " are essential to a cell ; the other, that cells 

 are usually formed independently of other cells ; 

 but, in 1839, it was a vast and clear gain to arrive 

 at the conception, that the vital functions of all 

 the higher animals and plants are the resultant of 

 the forces inherent in the innumerable minute cells 

 of which the}^ are composed, and that each of them 

 is, itself, an equivalent of one of the lowest and 

 simplest of independent living beings — the Torula, 



From purely morphological investigations, Tur- 

 pin and Schwann, as we have seen, arrived at the 

 notion of the fundamental unity of structure of 

 living beings. And, before long, the researches of 

 chemists gradually led up to the conception of the 

 fundamental unity of their composition. 



So far back as 1803, Thenard pointed out, in 



^ [Later investigations have thrown an entirely new light 

 npon the structure and the functional importance of the 

 nucleus ; and have proved that Schwann did not over-estimate 

 Its iraportam^e. 1894.] 



