283 
1 882.] The New Facto r in Organic Development, 
has hitherto been dealt with, proposes the following law of 
functional adaptation : — “ With increased activity every 
organ increases merely in that dimension (or those dimen- 
sions) which subserve the augmented activity. Thus a 
muscle, which by increasing use may reach twofold its 
former thickness, does not gain appreciably in length. Thus 
functional hypertrophy does not occasion growth in all 
dimensions but in one or two only, and thus gives to a limb 
or to an entire animal new morphological characters. This 
transforming agency is facilitated, quantitatively supported, 
and complicated by its antithesis, the atrophy of inactivity, 
which is also subject to the same dimensional laws. But in 
order that these two principles may lead to transformations, 
permanent causes, which compel increased use or disuse, are 
necessary, and if the changes produced are to become here- 
ditary, such causes must continue for generations. Dr. 
Roux also discusses the effects of a qualitative functional 
adaptation, without which the animal organism wouldremain 
on the stage which it has inherited. In this connection he 
quotes the utterance of Schiller in “ Wallenstein 5 ' — “ It is 
the spirit which creates the body.” 
But there are also considerations, still more completely 
overlooked, which may be included under the common name 
of functional adaptation, and which bear upon the effects of 
function in modifying the internal structure of the organs. 
We find that Hermann Meyer* has detected what may be 
called a special architecture in the spongy tissue of bones, 
which always represents the lines of maximum pressure or 
strain to which the organ is exposed. Thus what may be 
called the bone-beams are so placed as to produce the 
greatest strength with the smallest expenditure of material. 
Other anatomists, J. Wolf, H. Wolfermann, Bardeleben, 
&c., have confirmed these observations and extended them 
to almost all the bones of man and of several other 
mammals. 
A teleologist (Paleyan) or the like, admitting these facets, 
would claim this very structure as proof of special design 
and of individual creation. But it has been discovered by 
J. Wolff and confirmed by Kastor, Martini, and L. Rabe 
that such structural peculiarities are not something fixed, 
inherited, and inborn, but are capable of modification accord- 
ing to circumstances. Thus, if a bone is fractured and re- 
united in a crooked position, the lines of greatest firmness 
disappear from their normal places and take up new positions 
u 
* Archiv fur Anatomie und Physiologie, 1869. 
