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 tin' 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 1 839, 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 245, 

 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 (181 7-1905) was one 

 of the greatest histologists of the nineteenth century. He is a 

 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 181 7 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. 



