DIFFERENTIAL DIAGNOSIS 479 



prostrated, the only evidence of life being a slight respiratory 

 movement. The head occupies different positions. In .some it 

 is drawn backward as in tetanus ; in others it is drawn down 

 with the nose near the fore legs ; and in still others it is 

 extended as if the animal were .sleeping. The period of this 

 complete paralysis varies from a few hours to a few days, but 

 ordinarily it does not exceed twenty-four hours. Although 

 these animals are unable to move voluntarily, there is a reflex 

 action of the limbs until a very short time before death. 



During the period of incubation the temperature of the 

 rabbit is normal. As the time approaches for the first symp- 

 toms to appear there is an elevation of temperature of from i 

 to 2 degrees, which continues for a variable length of time, 

 but rarely longer than two days. This is followed by a grad- 

 ual or usually a more rapid drop to the subnormal, which con- 

 tinues to the end. 



The differential diagnosis in experimental animals is not 

 difficult. Rabbits inoculated with several varieties of patho- 

 genic bacteria frequently exhibit symptoms of paralysis for a 

 brief period preceding death. In cases of injury to the brain 

 or .spinal cord there may be paralysis, which in the absence of 

 the history of the case might be taken for that of rabies. In 

 these cases, however, the symptoms appear very soon after 

 inoculation. This is especially true when the paralysis is due 

 to mechanical injury of the brain or to irritation of septic sub- 

 stances. In the case of the pathogenic bacteria if paralysis 

 occurs at all it is almost invariably preceded by marked disa- 

 bility. This method of diagnosing rabies requires that the 

 inoculated animals remain apparently well for a considerable 

 length of time after the subdural inoculation and before the 

 paralytic symptoms appear. 



The lesions found on the post-mortem examination are 

 also of much assistance in making a diagnosis. If the animal 

 died from .septicemia or brain injury there will be lesions 

 almost invariably recognizable in the brain or viscera. In the 

 case of septicemia a bacteriological examination will reveal the 

 presence of microorganisms. If the death was caused by 



