285 
of Edinhurgli, Session 1883 - 84 . 
certain definite and investigable lines. These modifications would 
still of course be largely determined by modification in the environ- 
ment, yet the change of view is considerable. On the former view 
the organism is a plastic but essentially inert mass, yielding pas- 
sively to the forces of the environment ; on the latter, it is an active 
community, of which some or many members, under the influence 
of any favourable change of conditions, or the removal of any 
restraints, external or internal, immediately press into other positions 
and functions, which however apparently new, are either specialisa- 
tions of the existing, or reversions to an earlier type. 
Variation and disease are thus most closely akin ; for since all 
variations are ultimately cellular, pathological changes are simply 
definable as those variations which happen not to be conducive to 
success in the struggle for existence. And thus we might proceed 
further and further with the discussion of aetiology. 
The preceding theory then, although its range of application, un- 
limited in the scale of organic nature, may at first sight alarm the 
specialist, is actually founded on a simple but solid basis of observed 
facts ; it has been seen fairly to meet and co-ordinate the very 
numerous and hitherto, for the most part quite unrelated problems 
which were enumerated at the outset, and even to be applicable to 
numerous minor and unexpected problems which these suggested. 
And thus, were it even viewed from the standpoint of mathematical 
probability alone, it has received the most overwhelming verification. 
{Explanation of the Plate at page 292. ) 
II. An Hypothesis of Cell Structure. 
1. Statement of the Prohlem . — Great attention has, especially of 
recent years, been paid to the problem of cell structure, and a vast 
body of observations have been accumulated. Of these many are 
generalised; many, however, still remain unco-ordinated, and an 
hypothesis which attempts at once to unify these, to throw light 
upon the structural and functional aspects of contractile protoplasm, 
and to unite all these with that theory of the cell-cycle above pro- 
pounded, is therefore not untimely, and may, even if not completely 
exhaustive or satisfactory, be at least suggestive of a better explana- 
tion. Let us survey a few of the main peculiarities of protoplasmic 
structure which any such hypothesis must aim at unifying. 
