DIFFERKNTIAL DIAGNOSIS 481 



successfully in the Laboratory of the Pennsylvania State Live 

 Stock Sanitary Board. He reported its use in 52 cases. We 

 have used this method with success. 



We have found the plexiform ganglion, which is situated 

 just outside of the cranial cavity near the foramen lacerum 

 basis cranii, on the pneumogastric nerve, the most convenient 

 and the most desirable for study. The removal of this gang- 

 lion is comparatively easy and simple. 



There are two ways by which this ganglion can be easily found : 



1. Take up the pneumogastric nerve and trace it anteriorly to the 

 point where it enters the cranium. Near this point a slight enlarge- 

 ment, the ganglion of the trunk of the vagus, will be found. 



2. Cut through the skin from the mandibular symphysis posteri- 

 orly 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 gang- 

 lion. 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 as the ganglion is removed it is placed in 

 Flemming's fluid or in a standard aqueous solution of mercuric chloride 

 for a few hours, washed in water, carried through the alcohols and sec- 

 tioned by the paraffin method. With this method of fixation it is 

 almost imperative that the sections be stained with iron or Dela- 

 field's hematoxylin, of which we have found the latter the most 

 convenient. Alcohol, either 95 per cent, or absolute, may be used as a 

 fixer, in which case other st'aining methods may be used. However, 

 the fixation by this method is not as good, but it admits of a trifle more 

 haste. 



Normally this ganglion is composed of a fibrous capsule from which 

 a supporting fibrous tissue extends into the interior, holding in its 

 meshes the nerve cells, each of which is enclosed in an endothelial cap- 

 sule. The changes characteristic of rabies consist in the atrophy, the 

 invasion and the destruction of the ganglion cell as a result of new 

 formed cells, evidently from the endothelial capsule. These cells appear 



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