The Organism and Its Cells 1G9 



in the first mentioned view, though the methods of experi- 

 mentation employed were not such as to make it possible 

 for him to see the actual outgrowth of the fibers. He there- 

 fore tried to find a way of keeping sufficiently small isolated 

 bits of the embryonal neural tube to enable him to observe 

 the growths under the microscope if they actually occur. 



A summary of his results stated in his own words is : 

 "Pieces of undifferentiated embryonic tissue, when isolated 

 under aseptic precautions in clotted lymph, will live for 

 weeks and undergo at least the initial stages of normal his- 

 tological differentiation : cells from the axial mesoderm 

 give rise to striated muscle fibers ; epidermal cells form a 

 cuticular border; typical cliromatophores and a mesenchyme- 

 like tissue are formed from pieces containing portions of the 

 neural tube and axial mesoderm ; the walls of the neural 

 tube and the primordia of the cranial ganglia give rise to 

 long hyaline filaments closely resembling embryonic nerve 

 fibers. 



"Tissues grown in lymph function characteristically, as 

 is seen in the movement of cilia and the contraction of muscle 

 fibers when left in organic continuity with fragments of the 

 neural tube." . . . "The experiments show that neuroblasts 

 are competent to form primitive nerve fibers within a foreign 

 unorganized medium simply by the amoeboid outgrowth of 

 their protoplasm. By eliminating from the periphery all 

 formed structures which have heretofore been supposed to 

 transform themselves into nerve fibers and leaving only 

 the neuroblasts in the field, it is demonstrated that the lat- 

 ter are the sole elements essential to the formation of nerves. 

 The concepts of both Hensen and Held are rendered un- 

 tenable." -^ 



Thus a developmental point of capital importance which 

 had been debated at length and with considerable spirit as 

 long as investigation was conducted upon the organism in 

 its entire state, was solved by separating from the rest a few 



