288 The Nature of Biological Diversity 



c. Response of sympathetic nerve cells 

 oi chick embryos to implantation 

 of mouse sarcomas and to the injection 

 of other nerve yrotvth factors 



Since the heginning of this investigation in 1950, we realized that 

 the sympathetic nerve cells are far more affected by the tumoral fac- 

 tor than the sensory nerve cells. While the size increase of the sensory 

 ganglia adjacent to the transplant ranges between two and three times 

 that of the controls, the size increase of sympathetic ganglia is 

 four to six times that of the controls (42 ) . Two factors may in part 

 account for these differences: (1) The sympathetic nerve cells at 

 variance with the sensory nerve cells are all receptive to the nerve 

 growth factor; and (2) the effect is not restricted to a given period 

 of their differentiation but continues till the end of the incubation 

 time. As will be shown below, sympathetic nerve cells of mammals 

 remain receptive to the growth factor throughout all life (Fig. 28) . 



In a number of cases the effects of the tumor are restricted to the 

 sympathetic ganglia which establish contact with the neoplastic tissue 

 through their nerve fibers (35) . In the majority of the cases, however 

 (about 85 per cent of the total number of embryos examined, which 

 amounts to many hundreds), the entire sympathetic chain ganglia 

 are strikingly enlarged (36). Nerve fibers emerging from the hyper- 

 trophic and hyperplastic glanglia overflow the adjacent viscera, which 

 are not innervated in corresponding developmental stages in control 

 embryos; they also enter and fill large blood vessels with thick nerve 

 bundles. Fragments of tumor transplanted onto the chorioallantoic 

 membrane of 4- to 6-day chick embryos elicit the same effects. In this 

 last group of experiments, the tumor and the host share the circula- 

 tion, but no direct contact is established betwen them. 



Sympathetic ganglia from 9- to 11-day chick embryos, explanted in 

 vitro in proximity to fragments of mouse sarcomas, produce a dense 

 halo of nerve fibers similar to the halo produced by sensory ganglia 

 (see page 285) . The in vitro technique was also used to test the effects 

 of the purified extract of mouse salivary glands and of snake venom 

 on the sympathetic ganglia of chick embryos. The injection of the 

 purified extract of the salivary gland into the yolk of 6- to 10-day chick 

 embryos evokes an overgrowth of the entire sympathetic chain ganglia 

 and hyperneurotization of the viscera (43) . 



In summary, we may conclude that the M-D sensory neurons and 

 the sympathetic nerve cells of the chick embryos are highly receptive 



