398 RABIES 
with other diseases without finding Negri bodies or similar forms. 
He therefore holds these bodies as specific for rabies and the diagnosis 
as assured if they are found. Later writers agree with this conclusion. 
Examination for Negri bodies. At least four preparations from each of the hippo- 
campi, four from each of the cerebra, and four from the cerebellum, should be carefully 
examined before pronouncing the case negative. In making the preparations for 
examination any one of the following three methods may be employed: 
(a) Smear preparations as described by Dr. Williams, of the New York City Board 
of Health Research Laboratory. 
(b) Impression preparations as described by Dr. Frothingham, of Harvard Univer- 
sity. 
(ec) Fixing the tissue and making sections. 
Either of the first two methods is preferable to the last, although occasionally the 
Negri bodies seem to be more clearly differentiated in the section. Zenker’s fluid is 
recommended for fixing the tissue. It does not seem to be necessary to fix for more than 
from four to six hours when the tissues are cut in thin pieces. 
The stain to be employed for smear or impression preparations should be either 
Van Giessen’s, or eosin and methylene blue. If the tissue is fixed in acetone and 
sectioned, the staining method recommended by Mann or that proposed by Lentz gives 
excellent results. If the tissue is fixed in Zenker’s fluid, eosin and methylene blue 
should be used. 
Diagnosis by histological examination of the ganglia (specific 
tissue changes). The rapid diagnosis by means of the histological 
changes pointed out by Van Gehuchten and Nélis has been very 
successful in the experience of a number of workers. 
We have found the plexiform ganglion, which is situated just out- 
side of the cranial cavity near the foramen lacerum basis crani, on 
the pneumogastric nerve, the most convenient and the most desirable 
for study. The removal of this ganglion is comparatively easy and 
simple. 
There are two ways by which this ganglion can be easily found: 
Take up the pnéumogastric nerve and trace it anteriorly to the point where it enters 
the cranium. Near this point a slight enlargement, the ganglion of the trunk of the 
vagus, will be found. 
Cut through the skin from the mandibular symphysis posteriorly along the neck and 
reflect it back. An incision is then made through the mylohyoid muscle near the inner 
face of the mandible posteriorly past the digastric muscle and superiorly until the 
lingual nerve going to the tongue is exposed. ‘Trace this posteriorly until the point 
where it enters the cranium together with the vagus is reached. In this way it is easy 
to locate the vagus nerve and the plexiform ganglion. We have found either one of 
these methods or a combination of the two very convenient, and with a knowledge of the 
location of these parts there is no reason why the ganglion should not be removed quickly 
and easily. 
After the ganglion is removed there are a variety of methods which may be used in 
fixation and staining. The following we have found to be very satisfactory. As soon 
