CHAPTER II. 



CELL THEORY BEFORE 1860. 



THE progress of physiological knowledge from the 

 time of Fletcher may be said to be bound up in the 

 history of the cellular theory, which may be con- 

 sidered practically to have begun in 1838, when the 

 microscope was sufficiently perfected to give a solid 

 basis for the observation of facts. The hypothetical 

 anticipation of it by various authors in preceding 

 times, although interesting, need not detain us, and I 

 may merely refer those desirous of studying it to Pro- 

 fessor James Tyson's excellent work on the cell doc- 

 trine. Taking up the subject from 1838, I will 

 endeavour to select from the bewildering mass of 

 details and conflicting statements which have accumu- 

 lated since then those points which have a definite 

 bearing on the principles of the question. This may 

 be best done by tracing the cell doctrine in its com- 

 plete form up to the time when the cell was generally 

 accepted as the ultimate elementary unit of life; 

 then, by tracing again from the beginning the doc- 

 trine which is believed by many to have now sup- 

 planted it, viz., that the place of the cell is to be 

 taken by one of its constituents the protoplasm. 



