THE BIRTH OF HISTOLOGY 171 
now become a separate division of the science of anatomy, 
and engages the attention of a very large number of workers. 
While the men who built upon Bichat’s foundation are nu- 
merous, we shall select for especial mention only a few of the 
more notable, as Schwann, Koelliker, Schultze, Virchow, 
Leydig, and Ramon y Cajal, whose researches stand in the 
direct line of development of the ideas promulgated by 
Bichat. 
Schwann.—Schwann’s cell-theory was the result of close 
attention to the microscopic structure of the tissues of ani- 
mals. It was an extension of the knowledge of the tissues 
which Bichat distinguished and so thoroughly investigated 
from other points of view. The cell-theory, which took rise 
in 1839, was itself epoch-making, and the science of general 
anatomy was influenced by it as deeply as was the science of 
embryology. The leading founder of this theory was 
Theodor Schwann, whose portrait is shown on page 248, 
where there is also a more extended account of his labors in 
connection with the cell-theory. Had not the life of Bichat 
been cut off in his early manhood, he might well have lived 
to see this great discovery added to his own. 
Koelliker.—Albrecht von Koelliker (1817-1905) was one 
of the greatest histologists of the nineteenth century. He isa 
striking figure in the development of biology in a general way, 
distinguished as an embryologist, as a histologist, and in 
other connections. During his long life, from 1817 to 1905, 
he made an astounding number of additions to our knowledge 
of microscopic anatomy. In the early years of his scientific 
activity, ‘“he helped in establishing the cell-theory, he traced 
the origin of tissues from the segmenting ovum through the 
developing embryo, he demonstrated the continuity between 
nerve-fibers and nerve-cells of vertebrates (1845), . . . and 
much more.” He is mentioned further, in connection with 
the rise of embryology, in Chapter X. 
