THE STRUCTURE OF PROTOPLASM. 17 



structural element in the cell, and I am therefore thoroughly in 

 accord with those who have insisted that life in its full sense is 

 the property of the cell-system as a whole rather than of any 

 one of its separate elements. Nevertheless, we are perhaps 

 justified in maintaining that the continuous substance is the 

 most constant and active element, and that which forms the 

 fundamental basis of the system, transforming itself into gran- 

 ules, drops, fibrillae or networks in accordance with varying 

 physiological needs. 1 



Whether any or all of these elements are " living" or "life- 

 less " depends largely on the sense in which these words are 

 used ; and it is well, therefore, to follow the example of Sachs, 

 in substituting for these words, as applied to special structural 

 elements of the cell, the terms "active" and "passive," which 

 properly admit of degrees of comparison. The distinction 

 between "protoplasmic" (active) and " metaplasmic " or "para- 

 plasmic" (passive) elements, though a real and necessary one, 

 thus becomes, after all, one of degree only. 



We are thus brought to consider another point of some inter- 

 est suggested by the comparative study of the facts described 

 above. Butschli states that in the true or finer alveolar struc- 

 ture, characteristic of protoplasm in general, the alveoli do not 

 measure more than 2.0 microns, and as a rule are considerably 

 smaller. This, he insists, is not to be confounded with a 

 "coarser vacuolization," characterized by larger drops or spheres, 

 which may secondarily arise in the finer structure. Again, 

 Reinke and Waldeyer in a somewhat similar manner character- 

 ize as " pseudo-alveolar " a structure arising secondarily through 

 the deposit of passive metaplasmic products of metabolism, such 

 as yolk-spheres, fat-drops, and the like, in the living proto- 

 plasmic basis. Both distinctions break down, I think, in the 

 light of the foregoing facts. In most of the forms considered, 

 Arbacia, Toxopneustes, Echinarachnius, Asterias, the alve- 

 olar spheres are considerably less than 2.0 microns (i.o to 1.7), 



1 It is hardly necessary to state that this view is not original, except in so far 

 as it has been directly suggested by the observations described above ; for it has 

 been more or less definitely maintained by many others, and I am only expressing 

 what seems to be a growing opinion among workers in this field. 



