84 NATURE AND LIFE. 
pletely sheathed in the former. The lymph circulates with 
its globules between the inner surface of the lymphatic and 
the outer surface of the capillary, which occupies the cen- 
tre. The texture of the marrow of the bones, the placenta, 
the umbilical vesicle, the skin, the arteries, the pancreas, 
has been illuminated with strong light by the investiga- 
tions of the same observer. It may even be said that, of 
the thirty tissues of the system, there is not one whose 
nature is not better understood through his labors. And 
this work performed has suggested another to him: we 
mean the comparison of the same organic parts with each 
other at different times in their existence; that is to say, 
the establishment of general comparative anatomy. In this 
vast field of histological comparison, so little explored be- 
fore his time, Robin has collected many precious truths for 
the general science of biology. 
We have seen that the normal tissues of the organism 
consist of a fundamental anatomical element and of a cer- 
tain number of accessory elements. Medical art has gained 
wholly unexpected light from the discovery of this order 
of facts. The works of modern micrographers, particularly 
those of Hannover, Lebert, Virchow, Robin, Broca, Follin, 
etc., have proved, in fact, that all morbid growths, and 
especially those known under the names of tumors, cysts, 
polypi, cancers, tubercles, and scirrhous growths, proceed 
merely from the superabundant, excessive formation of 
some one of these accessory elements. It is now demon- 
strated that those new formations, so often repulsive in ap- 
pearance, and concealing the seeds of death, contain nothing 
which is foreign to the organization in its sound state, and 
are not characterized by any peculiar substance produced 
under the influence of the disease. They are due some- 
times to hypergenesis, that is, to an unusual collection of 
some accessory element taking part in the regular composi- 
tion cf the tissue in which they are developed; sometimes 
