638 ACTIVE IMMUNIZATION 



to the central nervous tissue, and, as in tetanus, the symptoms of the 

 disease are due to involvement of these tissues. 



The period of incubation, or the time elapsing between the time of 

 injury and the first symptoms, is quite variable, ranging from twenty 

 to sixty days, although it may be as short as ten days. As in tetanus, 

 this period depends upon (a) the location of the injury; (b) the quantity 

 or dose of virus ; (c) the kind of animal responsible for the injury. Bites 

 about the face and fingers, especially if they are deep and lacerating, 

 are especially dangerous; bites about the back and lower limbs, espe- 

 cially if superficial, are much less dangerous, and accompanied by a 

 longer period of incubation. It is to be remembered that bites may be 

 infectious as early as nine days before the dog shows well-marked symp- 

 toms of the disease. Not infrequently an animal is observed to be 

 surly and snappy for several days before rabid symptoms develop, and 

 a bite during this time should be regarded as dangerous. 



Only about 16 per cent, of human beings bitten by rabid animals and 

 untreated appear to contract rabies. Since the establishment of the 

 Pasteur treatment of the disease, the percentage of developed cases 

 after bites is much lower about 0.46 per cent. 



Diagnosis and Management of Rabies. Even though an animal 

 is unmistakably rabic, every effort should be made to destroy the animal, 

 not only in order to prevent further damage, but to corroborate the 

 diagnosis by microscopic examination of the nervous tissues for Negri 

 bodies. 



1. As a general rule, all animal bites should receive surgical attention. 

 Wounds produced by animals clinically rabid should be cauterized at 

 once with fuming nitric acid or pure phenol. This is done to offset 

 the delay in securing the Pasteur treatment, and because there is evi- 

 dence to show that thorough cauterization of the wound is in itself 

 highly beneficial. 



2. The animal should be promptly destroyed, not only to prevent 

 further damage, but in order to make a microscopic diagnosis by ex- 

 amination of the brain for Negri bodies. This examination is highly 

 important and should never be omitted, for if it shows the absence of 

 bodies, this fact should be carefully impressed upon the patient, as 

 there is no doubt that a neurotic element, amounting in many instances 

 to actual hysteria, may cause considerable harm to the patient even 

 though he is definitely free from rabic infection. 



3. The whole dog may be packed in ice and shipped at once to a 

 central laboratory, or the head alone may be removed and packed in 



