CONSERVATION AND CORRELATION OF VITAL FORCE. 339 
bility of the body at any given moment being perhaps of fixed 
amount; so that with regard to excitement, just as with regard to 
blood-supply, plus in one organ would imply minus in another.”* 
am unable to say just what views were entertained on this 
subject by Geoffroy Saint-Hilaire : — not having access to his 
writings. Milne-Edwards gives the following clear statement of 
his own opinion. ‘The principle of connection of organs regu- 
lating the place occupied by each; a tendency to an organic bal- 
ancement, equipoise, or compensation when the development of an 
organ acts, as it were, injuriously upon others, as if the amount of 
vital force were restricted and limited.t” 
Finally, I quote the following at second hand from Meckel. It 
seems almost too strange to be true, but as the authority is above 
reproach we can only accept it as a fact. Let it be observed that 
here, however, “ this antithesis extends over different children of 
one and the same mother. A girl had on each extremity a super- 
fluous digit, and one hand of her sister wanted four, being the 
number of digits which her sister had in excess, reckoning the four 
extremities together. ł ” 
These are a few out of the immense mass of similar illustrations 
I might bring forward in support of my belief in an absolute law 
at the bottom of these correlations of structure, and may I not 
add :— often of function? 
There are many facts on the other hand, which seem to militate 
against it. But it appears to me most likely that as we more 
thoroughly understand the principles of biology, in the same meas- 
ure will our exceedingly vague ideas on this subject become more 
determined and absolute :—in fact the evidence must almost of 
 hecessity, like that in favor of the theory of gravitation, become of 
. 
a cumulative character. Any other supposition would imply a 
belief in the ancient idea of a lusus naturé, which is opposed to 
the most firmly grounded dogmas of modern science. 
Any decided deductions in the way of distinct propositions con- 
cerning this law are as yet premature, but the following may 
find some support in the cases I have already given :— 
Ist. That organs anatomically or physiologically related tend 
to compensate among themselves for any aberration of structure 
or function. 
it p. 81. 
tManual of Zoology. Translated by R. Knox, edited by Blake, edition 1863, p. 200, 
‘Cyclopedia of Anatomy and Physiology, Vol. iv, part 2d. p. 946. 
