LAMARCK S THEORY OF EVOLUTION 207, 
makes the functions of other organs to be diminished 
in power. 
“Thus not only every organ or every part of the 
body, whether of man or of animals, being for a long 
period and more vigorously exercised than the others, 
has acquired a power and facility of action that the 
same organ could not have had before, and that it has 
never had in individuals which have exercised less, 
but also we consequently remark that the excessive 
employment of this organ diminishes the functions of 
the others and proportionately enfeebles them. 
“The man who habitually and vigorously exercises 
the organ of his intelligence develops and acquires a 
great facility of attention, of aptitude for thought, 
etc., but he has a feeble stomach and strongly limited 
muscular powers. He, on the contrary, who thinks 
little does not easily, and then only momentarily fixes 
his attention, while habitually giving much exercise 
to his muscular organs, has much vigor, possesses an 
excellent digestion, and is not given to the abstemi- 
ousness of the savant and man of letters. 
“ Moreover, when one exercises long and vigorously 
an organ or system of organs, the active forces of 
life (in my opinion, the nervous fluid) have taken such 
a habit of acting ( forter) towards this organ that they 
have formed in the individual an inclination to con- 
tinue to exercise which it is difficult for it to over- 
come. 
“Hence it happens that the more we exercise an 
organ, the more we use it with facility, the more does 
it result that we perceive the need (4esozz) of continu- 
ing to use it at the times when it is placed in action. 
So we remark that the habit of study, of application, 
of work, or of any other exercise of our organs or of 
any one of our organs, becomes with time an indis- 
pensable need to the individual, and often a passion 
which it does not know how to overcome. 
“ Thirdly, finally, the effort made by necessity to 
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