320 RABIES 



a supporting tissue holding in its meshes the nerve cells, each 

 one of which is enclosed in a capsule, made up of a single 

 layer of endothelial cells. The action of the rabic virus seems 

 to exercise its effect on these cells particularly, bringing about 

 an abundant multiplication of the cells forming this capsule, 

 leading finally to the complete destruction of the normal 

 ganglion cell and leaving in its place a collection of round 

 cells. Ordinarily a considerable number of ganglion cells will 

 be found which have undergone only a slight change, but 

 under certain conditions the process is so widespread that all 

 the ganglia cells are destroyed. The intensitj' of these changes 

 varies in different animals; thej- are perhaps most pronounced 

 in the dog, less marked in man and still less in the rabbit. 



Much of the value of these findings consists in their mak- 

 ing a sure and quick means of diagnosis. It is possible to com- 

 plete the examination within six hours after the death of the 

 animal, and under ordinary circumstances a positive opinion 

 can be given in from 24 to 36 hours. It is important that the 

 animal should be allowed to die and not be killed prematurely, 

 as where the disease is not permitted to run its full course end- 

 ing in death, the changes may be absent or only slightlj' 

 developed. 



i^ 242. Differential diagnosis. From the often obscure 

 manner of infection, the long period of incubation, the vari- 

 able symptoms and the absence of gross morbid changes char- 

 acteristic of the disease, it is easy to mistake rabies for various 

 other nervous disorders and vice versa, unless a definite method 

 of diagnosis can be availed of. 



Diagnosis by animal inoailatioii. The method which the 

 experience of pathologists has shown to be the best, is the sub- 

 dural inoculation of rabbits with a suspension of the brain or 

 spinal cord of the su.spected animal. The subdural inoculation 

 with the brain tissue of rabid animals was first demonstrated 

 by Pasteur to be more reliable and more rapid in its results 

 than the subcutaneous injections. The procedure is simple. 

 The brain of the suspected animal is removed with aseptic 

 precautions as soon as possible after death. A small piece of 

 the brain or spinal cord is placed in a sterile mortar aud thor- 



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