300 LAMARCK, HIS LIFE AND WORK 
“Moreover, owing to these diverse influences, the 
faculties increase and become stronger by use, become 
differentiated by the new habits preserved for long 
ages, and insensibly the organization, the consistence 
—in a word, the nature and condition of parts, as also 
of the organs—participate in the results of all these 
influences, become preserved, and are propagated by 
generation. 
“These truths, which are only the results of the two 
natural laws above stated, are in every case com- 
pletely confirmed by facts; they clearly indicate the 
course of nature in all the diversity of its products. 
“ But instead of contenting ourselves with generali- 
ties which might be considered as hypothetical, let 
us directly examine the facts, and consider, in the 
animals, the result of the use or disuse of their organs 
on the organs themselves, according to the habits 
that each race has been compelled to contract. 
“T shall now attempt to prove that the constant 
lack of exercise of organs at first diminishes their 
faculties, gradually impoverishes them, and ends by 
making them disappear, or even causing them to be 
atrophied, if this lack of use is perpetuated for a very 
lous time through successive generations of animals 
of the same race. 
‘“‘T shall next prove that, on the contrary, the habit 
of exercising an organ, in every animal which has not 
attained Ane limit ior the diminution of its faculties, 
not only perfects and increases the faculties of this 
organ, but, besides, enables it to acquire developments 
and dimensions which insensibly change it; so that 
with time it renders it very different from the same 
organ in another animal which exercises it much less. 
“ The lack of use of an organ, become constant by the 
habits formed, gradually impoverishes this organ, and 
ends by causing tt to disappear and even to destroy tt. 
it Ne sucha proposition can only be admitted on 
proof, and not by its simple announcement, let us 
