308 ANTHRAX; AND HYDROPHOBIA. 



come into direct contact with the wound.. Whatever the 

 poison may be, it is evidently, elaborated in the salivary 

 glands, the parotid gland being the one most involved The 

 secretions of the lachrymal, adrenal, and mammary glands, 

 and the pancreas, may also contain the virus. The brain 

 and spinal cord, especially the medulla oblongata, are highly 

 virulent. The virus has never been found in the blood, urine, 

 or aqueous humor of the eye. 



As in the case of tetanus, the virus of rabies has a selective 

 action on the nerve tissues in general and the central nervous 

 system in particular. 



The symptoms are not manifested immediately after the 

 injury, but after a definite period of incubation, during which 

 the causative germ is elaborating its toxin. 



The period of incubation and the severity of the disease are 

 dependent upon several factors. The usual period of incu- 

 bation is from twenty to sixty days ; but several cases have 

 been reported in which the period of incubation lasted for 

 several months. The factors which influence the incubative 

 period are, first, the character and location of the wound ; 

 second, the amount of virus introduced into the body ; third, 

 the virulence of the poison. 



The period of incubation is very short when the wound is 

 a lacerated one, especially of the face ; or when it is located in 

 some portion of the body that is well supplied with nerves, 

 such as the finger-tips; or where a large nerve-trunk is very 

 near to the injury, as at the elbow-joint. 



Slight or clean-cut wounds and wounds of the back are 

 usually followed by long periods of incubation ; and, in gen- 

 eral, deep wounds are followed by shorter periods of incuba- 

 tion than are superficial wounds. 



These facts would naturally lead to the conclusion that the 

 germ causing this disease is undoubtedly an anaerobic organism, 

 and that may account for the fact that it has not as yet 

 been discovered, for it may have to be grown in a certain 

 atmosphere. 



Infection : It has been determined experimentally that sub- 

 cutaneous injection of the virus is not productive of the dis- 

 ease unless the virus is injected deeply into a muscle or near 



