PROFESSOR VIRCHOW AND EVOLUTION. 637 
are the great agents of molecular disturbance. On the 
inert molecules of seed aiid soil these waves impinge, dis- 
turbing the atomic equilibrium, which there is an imme- 
diate effort to restore. The effort, incessantly defeated 
for the waves continue to pour in is incessantly renewed: 
in the molecular struggle matter is gathered from the soil 
and from the atmosphere, and built, in obedience to the 
forces which guide the molecules, into the special form of 
the tree. In a general way, therefore, the life of the tree 
might be defined as an unceasing effort to restore a dis- 
turbed equilibrium. In the building of crystals Nature 
makes her first structural effort; we have here the earliest 
groping of the so-called " vital force/' and the manifes- 
tations of this force in plants and animals, though, as 
already stated, indefinitely more complex, are to be re- 
garded of the same mechanical quality as those concerned 
in the building of the crystal. 
Consider the cycle of operations by which the seed pro- 
duces the plant, the plant the flower, the flower again the 
seed, the causal line, returning with the fidelity of a 
planetary orbit to its original point of departure. Who or 
what planned this molecular rhythm? We do not know 
science fails even to inform us whether it was ever " plan- 
ned " at all. Yonder butterfly has a spot of orange on its 
wing; and if we look at a drawing made a century ago, of 
one of the ancestors of that butterfly, we probably find the 
selfsame spot upon the wing. For a century the molecules 
have described their cycles. Butterflies have been begotten, 
have been born, and have died; still we find the molecular 
architecture unchanged. Who or what determined this 
persistency of recurrence? We do not know; but we stand 
within our intellectual range when we say that there is 
probably nothing in that wing which may not yet find its 
Newton to prove that the principles involved in its con- 
struction are qualitatively the same as those brought into 
play in the formation of the solar system. We may even 
take a step further, and affirm that the brain of man the 
organ of his reason without which he can neither think 
nor feel, is also an assemblage of molecules, acting and 
reacting according to law. Here, however, the methods 
pursued in mechanical science come to an end; and if 
asked to deduce from the physical interaction of the brain 
molecules the least of the phenomena of sensation or 
