284 The Nature of Biological Diversity 



Iff. Growth BSesponse of Nerve Cells 

 to a Diffusible Protein Agent 



The finding in 1948 by Bueker of a nerve growth stimulating effect 

 of mouse sarcoma 180 on the sensory ganglia of chick embryos (34) 

 may be defined as the outcome of a fortuitous discovery and a calcu- 

 lated search. The results so much exceeded the expectation that the 

 unprepared mind of the observer overlooked the exceptional magni- 

 tude of the response in the attempt to make it fit into the previously 

 accepted schemes of growth and differentiation in the nervous system. 



In transplanting a fragment of mouse sarcoma 180 in the body wall 

 of 3-day chick embryos, Bueker wanted to test the effect of a rapidly 

 expanding tissue on sensory and motor nerve cells. When he examined 

 the embryos 5 days later he found in a number of cases that the tumor 

 had become established and was invaded by sensory but not by motor 

 nerve fibers. He also observed that the sensory ganglia contributing 

 fibers to the tumor were enlarged in size as compared to the contra- 

 lateral normal ganglia. No changes were observed in the motor col- 

 umn. The author concluded that the tumor elicited the growth 

 response in the sensory ganglia by providing them with a larger field 

 of innervation than their usual field. Since the effect appeared to be 

 restricted to the ganglia sending nerve fibers to the tumor, the nerve 

 fibers were considered as the mediators of the effect. The results and 

 the conclusions therefore fitted well into the picture presented above 

 of the effect of the periphery on associated nerve centers. A reinvesti- 

 gation of this effect led to a different interpretation of the phenom- 

 enon. 



a. Response of sensory embryonic 

 nerve cells to implantation 

 of mouse sarcomas 



The response of the sensory ganglia to implantation of mouse 

 sarcoma 180 or 37 was investigated in a close series of chick embryos 

 ranging in age between 4 and 18 days (35). Ganglia adjacent to the 

 transplant provide its neurotization with large nerve bundles, which 

 branch in all directions inside the tumor (Fig. 25). At 11 days the 

 ganglia appear three times larger than controls. The overgrowth is 

 due to an increase in cell size and cell number of the M-D population, 

 whereas no changes are apparent in the V-L population, which does 

 not seem to participate in the innervation of the tumor (Fig. 24). 

 From the eleventh day to the end of the incubation period, the effect 



