382 Hydrophobia, Lyssa, or Rabies 



of symptoms is accepted as evidence that the central nervous 

 system has been reached. 



When as in experimental inoculation the virus is at once placed in 

 the central nervous system, symptoms do not at once develop, hence 

 it is concluded that not only must the essential parasites reach the 

 central nervous system, but they must do so in sufficient numbers 

 before enough damage can be done to produce the symptoms. 

 Under the most favorable conditions of infection, this requires about 

 six days. 



The virus is, however, not confined to the nervous system for the 

 saliva is infective, and the salivary glands, pancreas, and perhaps 

 other glands harbor the infective agent. How it reaches these 

 structures has not yet been determined. In them Negri bodies are 

 present but whether they reach the glands through the blood or by 

 way of their nerVous connections is not known. 



There is no morbid anatomy of rabies. Carefully made autopsies 

 upon the bodies of rabid human beings and animals show nothing 

 by which the nature of the disease can be determined. Most inter- 

 est naturally centers about the brain and spinal cord as being the 

 chief sources of disturbance and chief seats of the virus. There are, 

 however, so few changes as scarcely to merit description. In some 

 cases the meninges are distinctly congested, but in uncomphcated 

 cases there is no meningitis and therefore no inflammatory exudation. 



In a few cases there may be scattered minute hemorrhages! In 

 many cases there are no lesions. 



The pathologic histology of rabies reveals certain fairly constant 

 lesions described in the next section, but they are not now regarded 

 as characteristic of the disease. 



Diagnosis of Rabies. — ^There are three means of arriving at a 

 diagnosis of rabies in cases of suspected "mad dogs." 



The animal having been killed, its head is cut off by an incision 

 through the neck at some distance from the skull, and immediately 

 taken to an appropriate laboratory or carefully packed in plenty of 

 ice and sent to the laboratory by express. The fresher the tissue 

 received by the laboratory worker, the more certain his results 

 can be. 



Carefully opening the skuU of the dog, the brain is removed to a 

 sterile dish. Good sized bits of tissue are taken from the appropriate 

 portions of the brain and placed in glycerin for future inoculation 

 operations if necessary, small bits of the same tissue are spread upon 

 slides according to the "smear" method of WiUiams and Lowden, 

 or sUdes may be spread by the "adhesion" method of Frothmgham* 

 who makes an incision into the brain, lays it open in the appropriate 

 areas, and then applies the flat surface of a perfectly clean slide to 

 the flat cut surface of the brain. When the slide is hfted up (not 

 slid off), nerve-cells adhere to it, in which the Negri bodies may 

 * Jour. Med. Research, 1916, Xiv, 477. 



