304 BACTERIOLOGY FOR NURSES 



over the whole body. Generally the patient has full consciousness 

 between the attacks until the final stage of the disease. The 

 convulsive period lasts from one to four days and may be followed 

 by a paralytic stage lasting from two to eighteen hours. In the 

 majority of cases death occurs on the third or fourth day after 

 symptoms appear. 



Despite repeated investigations all attempts to discover the 

 causal agent of the disease were unsuccessful until in 1903 Negri 

 described certain round or angular bodies lying within the large 

 nerve cells or their processes, which he claimed were specific for 

 rabies and in all probability protozoan in character. Negri's 

 observations have been generally confirmed and the presence of 

 the bodies is accepted as diagnostic. 



Negri bodies may be detected in fresh tissue by means of the 

 smear method. Small pieces of gray matter are removed from 

 three different portions of the central nervous system : (1) from 

 the cortex in the region of the crucial sulcus ; (2) from Ammon's 

 horn, and (3) from the gray matter of the cerebellum. Minute 

 portions of the tissue are placed on well-cleaned slides, crushed 

 into a thin layer under a coverslip, after which the coverslip is 

 moved slowly and evenly along the slide, leaving a film of nerve 

 cells in its train. The smears are dried in the air and stained with 

 Giemsa's stain. When examined under the oil immersion lens 

 the organisms appear pale blue and within their protoplasm one 

 or several round or oval pink bodies may be seen. In addition, 

 both within the protoplasm and the pink-stained bodies small red 

 or violet granules occur singly or in clumps. 



Experiments have shown that the virus is filtrable. It is un- 

 harmed by freezing. On the other hand, it is readily destroyed 

 by drying and by direct sunlight and is rendered inert by exposure 

 for one hour to 50 C. When protected from heat, sunlight, and 

 air it retains its virulence for a long period. 



Pasteur in 1880 made the important discovery that rabies 

 may be prevented by immunization with gradually increasing 

 doses of the attenuated virus. So successful was his method of 

 treatment that with some modifications it is still used in all parts 



