426 MARTIN U. CHASE 



throup;li the thoracic vagus just above the bronchial rami, 

 sliows no normal myelinated fibers and only a few scattered 

 unmyelinated axones. There are present, however, a few bun- 

 dles of unmyelinated fibers which are clearly of sympathetic 

 origin. Th(y cling in groups and stain in a characteristic man- 

 ner. Similar groups of unmyelinated fibers, present at this level 

 in the normal vagus nerve, were readily identified as of sym- 

 pathetic origin by their contrast with the vagus fibers. They 

 occupy only a small part of the total cross section area. 



Sections taken below the pulmonary plexuses show the right 

 vagus to have retained its degenerated character. It is joined 

 early by twigs from the normal left vagus, whose deeply stained 

 fibers contrast sharply with the degenerated areas. It is im- 

 possible to locate in these sections the sympathetic fibers seen 

 at a higher level. They are not present in bundles, and it 

 would be impossible to differentiate individual sympathetic 

 fibers from normal fibers from the left vagus. 



CHANGES PRODUCED BY REMOVAL OF A PORTION OF THE 

 CERVICAL VAGO-SYMPATHETIC TRUNK 



In the animal from which the illustrations are taken, a por- 

 tion of the right sympathetic vagus trunk was removed as in- 

 dicated (fig. 1, B) and the dog was allowed to live four weeks. 



Figure 2 is a drawing from a cross section of the right vagus 

 trunk just proximal to the bronchial rami (fig. 1, 2, 3) stained 

 by the pyridine silver method. There are seen no normal myel- 

 inated or unmyelinated nerve fibers. The aggregations of 

 granules, surrounded by definite zones, are nuclei of neurilemma 

 cells, as is proven by longitudinal section. The entire cross 

 section shows the same structure, there being only an occasional 

 naked axone. There are no bundles of unmyelinated sympathetic 

 fibers as was seen at the same level in the specimen previously 

 described. 



Figin-e 3 is a drawing of a small part of a cross section of the 

 same nerve at about the same level, stained with osmic acid. 

 Note the presence of a number of deeply stained globules, which 

 are the remains of degenerated myelin sheaths. There is pres- 



