DIFFERENTIAL DIAGNOSIS 477 



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 gang- 

 lion 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 intensity of these changes 

 varies in different animals ; they are perhaps most pronounced 

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



Much of the practical value of these findings consists in 

 their making it possible to make a sure and quick diagnosis. 

 It is possible to complete the examination within six hours 

 after the death of the animal, and under ordinary circum- 

 stances 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 ending in death, the changes may be 

 absent or only slightly developed. 



§ 374. Differential diagnosis. From the often obscure 

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

 ble 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 inoculation. The method which the 

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

 dural inoculation of rabbits or guinea-pigs with a suspension 

 ' of the brain or spinal cord of the suspected animal. The sub- 

 dural 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 and thoroughly ground with a few cubic centi- 



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