IX THE HISTORY AND SCOPE OF ZOOLOGY 363 



minute investigation of structure and development 

 and that of zoo-chemistry and zoo-physics. He spent 

 a large part of the next forty years in an attempt to 

 penetrate further into the structure of cell-substance ; 

 he hoped to be able to find in cell-substance ultimate 

 visible molecules, a knowledge of the arrangement 

 and characters of which would explain the varying 

 properties of protoplasm. 



It is not a little remarkable that Schwann, who 

 thus brought about the union of physiological and 

 morphological study by his conception of cell-sub- 

 stance, should also have been the initiator of that 

 special kind of experimental investigation of the 

 physical properties of tissues by the exact methods 

 used by physicists which, by the aid of the kymo- 

 graphion, the thermo-electric pile, and the galvano- 

 meter, has been so largely pursued during the last 

 thirty years in our physiological laboratories. It is 

 perhaps less surprising that Schwann, who had so 

 vivid a conception of the activity and potentialities 

 of the cell-unit, should have been the discoverer of 

 the immensely important fact that putrefaction and 

 fermentation are not the consequences of death but 

 of life, and that without the presence of living Bacteria 

 putrefaction does not occur, whilst he also is the dis- 

 coverer of the fact that the yeast which causes alcoholic 

 fermentation is a mass of unicellular living organisms. 



From Schwann's time onward the cell became 

 more and more the point of observation and experi- 

 ment in the progress of both Morphography and Physi- 

 ology. It was soon shown, chiefly through Kolliker 



