THE GENERAL CONSTITUTION OF LIVING BEINGS. 7] 
been more or less confounded with the tissues. Neither 
their function nor their biological characteristics had been 
defined. Phenomena had been explained without ascend- 
ing to those corpuscles which are the seat of their begin- 
ning. This savant regarded them for the first time as 
properly forming the subject of a special branch of anat- 
omy. Besides, he discovered a certain number of them 
which had till then escaped microscopic observation—the 
perineura in the nerves, the medullocele and myeloplax in 
the marrow of the bones; he disclosed the unknown func- 
tions of several others, such as the leucocytes, the nerve- 
cellules of the ganglia, the different epithelia ; in a word, 
he shed new light upon the history of all by describing the 
peculiarities of their origin and development. 
Nothing is more instructive and attractive than the 
study of the anatomical elements. They are invisible to 
_ our eyes, but they are not the less the glowing centres in 
which the fire of life burns. It is in and by them that it 
begins and grows; it is in them that those fundamental 
attributes one after another appear, which occasion the 
highest manifestations of animal existence. Real micro- 
cosms, each living with its own self-subsisting life, they 
are endowed with essential properties which explain all 
vital acts. Their composition from immediate principles 
is quite complex. It is as inconstant as their structure is 
delicate ; subject to an incessant molecular renewal, assimi- 
lating constantly new materials, and constantly getting rid 
of a part of their substance, they are in a state of per- 
manent transmutation. This perpetual renovation is ex- 
actly nutrition, the positive mark of organized beings. No 
life without nutrition. The lowly vibrio nourishes itself as 
the most complete mammal does; the meanest mould-spot 
as the gigantic cedar. All other properties of living bod- 
ies are subordinated to this one, which is their first condi- 
tion, and the most specific sign of life. Another charac- 
