306 Manual of Veterinary Microbiology. 



fore amvins: at the center is itself shorter. How- 

 ever, under natural conditions the duration of this 

 latent period is influenced by various factors, such as 

 the quantity of the virus, the richness in nerves, and 

 the extent of the injury to these nerves. 



The action of the virus of rabies on the nerve cen- 

 ters and on the nerves is indirect ; this virus does not 

 act as a chemical a.s^ent would, strychnine, for exam- 

 ple. The anatomical changes, little visible to the naked 

 eye, appear under the microscope as inflammatory 

 lesions at difiJerent stages of their evolution. These 

 lesions have their seat principally in the nerves of the 

 bitten part and in the corresponding part of the spinal 

 cord. They consist of congestions and capillary 

 hemorrhages, with infiltration of leucocytes ; other 

 lesions observed are limited foci of necrosis, diverse 

 desrenerations of the central nerve cells, transforma- 

 tion of the myeline, hypertrophy of the axis cylin- 

 ders, etc. 



The rabid symptoms are the expression of the neu- 

 ritis and myelitis which successively develop. These, 

 changes manifest themselves by phenomena of excite- 

 ment or of depression according as they are more or 

 less advanced. Such phenomena are usually suc- 

 cessive in occurrence, but may appear separately ; 

 hence the two forms, furious rabies and dumb or 

 paralytic rabies. Most frequently they are combined, 

 and mixed forms result, intermediate between the two 

 preceding, thus establishing the unity of the disease. 

 The symptomatic tableau will naturally vary accord- 

 ing to the part of the cerebro-spinal axis first invaded, 

 and therefore according to the place of inoculation. 



The experiments of Pasteur, in which rabies was 



