172 LAMARCK, HIS LIFE AND WORK 
which then passes along the smallest nervous ramifi- 
cations in the substance of the nerve, which is a very 
good conductor for it. On its side the brain sends 
back the subtile fluid in question along the nerves to 
the different organs. 
In the same work (1802) Lamarck defines thought 
as a physical act taking place in the brain. ‘‘ This 
act of thinking gives rise to different displacements 
of the subtile nervous fluid and to different accumula- 
tions of this fluid in the parts of the brain where the 
ideas have been traced.”” There result from the flow of 
the fluid on the conserved impressions of ideas, special 
movements which portions of this fluid acquire with 
each impression, which give rise to compounds by 
their union producing new impressions on the delicate 
organ which receives them, and which constitute 
abstract ideas of all kinds, also the different acts of 
thought. 
All the acts which constitute thought are the com- 
parisons of ideas, both simple and complex, and the 
results of these comparisons are judgments. 
He then discusses the influence of the nervous fluid 
on the muscles, and also its influence considered as 
the cause of feeling (sex¢zment). Finally he concludes 
that feu jizxé, caloric, the nervous fluid, and’ the 
electric fluid “are only one and the same substance 
occurring in different states.” 
