28 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. 



contains a greater or smaller quantity of fluid, and that under 

 particular circumstances by contraction or shrinking- it may 

 thus be reduced to extremely small dimensions. 



Another question which remains to be solved is whether we 

 have grounds for admitting that, independently of the intra- 

 cellular fluid, there exist any differences in the structure of the 

 protoplasm. 



Optical examination has not as yet enabled us to draw any 

 conclusion on this point. Hitherto protoplasm has only been 

 observed to be a body refracting light singly; or, more cor- 

 rectly speaking, no part of it has been observed to possess 

 doubly refractive powers. When such a peculiarity has been 

 observed, the protoplasm has been considered to be modified 

 in order to fulfil some special purpose. 



I am myself inclined to believe that two functionally 

 different substances are present, and am supported in my 

 opinion by the circumstance that I have learnt to recognize 

 two active conditions : one in which the cell is dilated, as after 

 immersion in water ; and one in which it is contracted 

 (shortened). 



But even if the dilated condition, as on Hermann's hypothesis, 

 is to be regarded as the condition of rest, we must from this point 

 of view also admit the existence of two functionally different 

 substances. 



In the present state of science we must acknowledge that we 

 are unable to see any differentiation of parts under the micro- 

 scope, nor does experiment furnish us with any ground for 

 admitting the existence of a definite arrangement of parts differ- 

 ing in their physiological properties. At the same time, those 

 cells, or cell derivatives, must of course be excepted in which 

 we are able to recognize any definite peculiarities appearing to 

 be associated with the performance of a specific function. The 

 optical peculiarities of transversely striated muscular fibres, 

 and the apparent structure perceptible in ganglion cells, must 

 doubtless be regarded as dependent on differentiation of struc- 

 ture. Such instances as these are referrible to the class of 

 protoplasmic masses modified for the performance of some 

 special function. 



In reference to the boundaries of a cell, the state of our pre- 



