CHAPTER III. 



INFECTIOUS DISEASES WITH SPECIAL INVOLVE- 

 MENT OF THE NERVOUS SYSTEM. 



RABIES. 



■ Hydrophobia. Lyssa. 



Definition. —An acute infectious disease, fatal in the 

 majority of cases, and characterized clinically by disturb- 

 ance of consciousness, marked irritability and later by 

 symptoms of paralysis. 



Occurrence. — Kabies is one of the oldest known diseases 

 and has been observed in all countries. It is most com- 

 monly noted in dogs, cats, wolves and foxes. Other animals 

 are less commonly affected. It is estimated that about 

 90 per cent, of the cases of rabies occur in dogs. The 

 disease often occurs enzootically, which may be at any 

 season of the year. The larger number of outbreaks in the 

 United States has been in the colder months of the year. 

 Outbreaks are naturally more frequent where dogs congre- 

 gate, and in communities or cities where there are no pro- 

 tective regulations. In some countries and districts rabies 

 is decreasing, due to proper police regulations which restrict 

 the number of dogs running at large. 



Etiology.— Rabies is produced by an ultramicroscopic 

 virus. This virus is found to be the most virulent when 

 taken from the central nervous system (brain and cord), 

 less so from the peripheral nerves, salivary and other glands 

 and their secretions. The infection does not seem to be 

 present in the blood of affected animals. The infectious 

 agent is fixed, non-volatile and is an obligatory or fixed 

 parasite. 



Pathogenicity.— The disease is readily transmitted to 

 dogs, rabbits, guinea pigs and other animals by inoculating 



