THE FILTERABLE MICROBES 391 



symptoms before three weeks- and the onset may be delayed for 

 a year. In fact many persons and animals bitten by rabid dogs 

 may fail to develop the disease at all. This variability depends 

 upon the virulence and the amount of virus and especially upon 

 the part of the body into which it is introduced. Bites upon the 

 face or hands, because of the rich nerve supply and the lack of 

 protectionby clothing, are especially dangerous. After the dis- 

 ease has developed so as to cause symptoms, death is inevitable 

 in the present state of our knowledge. 



Rabies may be diagnosed in an animal by observing the course 

 of the disease, by autopsy and by inoculation of test animals and 

 observation of the course of the disease in them. If the sus- 

 pected animal be caged, the question of rabies may be settled in a 

 few days, for, if he is mad, the raging stage will be quickly followed 

 by the characteristic paralysis and death. If the animal has been 

 killed, a careful autopsy may reveal the absence of food from the 

 digestive tract and the presence there of abnormal ingested ma- 

 terial (grass, wood or stone), highly suggestive of rabies. Mi- 

 croscopic examination of the central nervous system may reveal 

 the Negri bodies, characteristic of the disease. For confirmation 

 of the diagnosis a portion of the brain or spinal cord, removed with- 

 out contamination, should be injected into the brain of guinea- 

 pigs and rabbits and the effects observed. This last test 

 carried out by an experienced observer is the most trustworthy 

 of all. 



The Pasteur treatment of rabies is designed to induce immu- 

 nity after the person has been bitten and before the disease has had 

 time to develop. Pasteur^ first demonstrated the possibility of 

 this by experimental work on dogs, and the subsequent use of 

 the method in man has been remarkably successful and the dis- 

 ease is practically always prevented if the treatment is begun 

 directly after infliction of the infecting wound. The first essen- 

 tial is thorough cauterization of the wound, best with concentrated 

 nitric acid under anesthesia. The patient is then injected sub- 

 1 Vallery-Radot : The Life of Pasteur, 1911, Vol. II, p. 188. 



