524 
alcohol containing 1 per cent of strong ammonia for 48 hours, rinsed 
in distilled water, put in pyridine for 24 hours, washed in many 
changes of distilled water 24 hours, placed in 2 per cent silver 
nitrate at 35° C in the dark for 3 days, rinsed in water, and placed 
for one day in a 4 per cent solution of pyrogallic acid in 5 per cent 
formalin. Sections are made in paraffin and after mounting are 
ready for examination. The results can sometimes be improved by 
a preliminary injection of 95 per cent alcohol, containing 1 per cent 
of ammonia, through the arteries till the tissue is thoroughly saturated 
after which it is dissected out and placed in ammoniated absolute 
alcohol (Huser 13). Huser has found this method of use in studying 
the cranial nerves of small animals and embryos, since the entire 
head can be decalcified, stained in toto and cut into serial sections 
with excellent results. 
The results of the application of the pyridine-silver technique to 
the vagus are shown in the accompanying figure. Medullated axons 
are stained yellow, and are surrounded by a colorless ring of myelin. 
Non-medullated fibers are stained black and are sharply differentiated 
from the light yellow endoneurium. 
The drawing was made from a section of the cervical trunk of 
the human vagus some distance below the nodose ganglion. It will 
be seen from a glance at this figure that non-medullated fibers are 
present in enormous numbers in the vagus nerve. These observations 
correspond to those made by CuHasE and Ranson ‘14 on the vagus 
of the dog. 
Because the fresh material was more easily obtained in the dog 
a more extensive study of the vagus was made in this animal. The 
roots, trunk and branches of the vagus were examined both in pyridine 
silver and in osmic acid preparations; and it was found that at all 
levels there- were great numbers of non-medullated fibers. Most of 
the large medullated fibers leave the vagus through the pharyngeal, 
superior laryngeal, and recurrent nerves while practically all of the 
non-medullated fibers are carried down into the thoracic vagus. Most 
of the medullated fibers in the thoracic vagus leave it through the 
bronchial and cesophageal branches, so that the vagus as it passes 
through the diaphragm is practically a non-medullated nerve. It is 
composed almost entirely of non-medullated axons and contains only 
a few scattered medullated fibers. 
